diff --git a/changelog/fix-10149-csv-export-dash-separated-locales-not-working b/changelog/fix-10149-csv-export-dash-separated-locales-not-working
new file mode 100644
index 00000000000..970c629a5a5
--- /dev/null
+++ b/changelog/fix-10149-csv-export-dash-separated-locales-not-working
@@ -0,0 +1,4 @@
+Significance: patch
+Type: fix
+
+Provide correct language code when requesting CSV exports in a region-specific language
diff --git a/client/data/deposits/resolvers.js b/client/data/deposits/resolvers.js
index dd815282329..a4a0ad14e26 100644
--- a/client/data/deposits/resolvers.js
+++ b/client/data/deposits/resolvers.js
@@ -84,7 +84,7 @@ const formatQueryFilters = ( query ) => ( {
 	],
 	status_is: query.statusIs,
 	status_is_not: query.statusIsNot,
-	locale: query.userLocale,
+	locale: query.locale,
 } );
 
 export function getDepositsCSV( query ) {
diff --git a/client/data/disputes/resolvers.js b/client/data/disputes/resolvers.js
index ccc72c001f3..ce748a46562 100644
--- a/client/data/disputes/resolvers.js
+++ b/client/data/disputes/resolvers.js
@@ -38,7 +38,7 @@ const formatQueryFilters = ( query ) => ( {
 			: query.search,
 	status_is: query.statusIs,
 	status_is_not: query.statusIsNot,
-	locale: query.userLocale,
+	locale: query.locale,
 } );
 
 export function getDisputesCSV( query ) {
diff --git a/client/data/transactions/resolvers.js b/client/data/transactions/resolvers.js
index 54d96fb7127..37b1c94fb0d 100644
--- a/client/data/transactions/resolvers.js
+++ b/client/data/transactions/resolvers.js
@@ -58,7 +58,7 @@ export const formatQueryFilters = ( query ) => ( {
 	source_is_not: query.sourceIsNot,
 	search: query.search,
 	user_timezone: getUserTimeZone(),
-	locale: query.userLocale,
+	locale: query.locale,
 } );
 
 /**
diff --git a/client/deposits/list/index.tsx b/client/deposits/list/index.tsx
index 22a1532dcc4..0420c4bcfd8 100644
--- a/client/deposits/list/index.tsx
+++ b/client/deposits/list/index.tsx
@@ -214,7 +214,7 @@ export const DepositsList = (): JSX.Element => {
 
 	const endpointExport = async () => {
 		const userEmail = wcpaySettings.currentUserEmail;
-		const userLocale = wcpaySettings.userLocale.code;
+		const locale = wcSettings.locale.userLocale;
 
 		const {
 			date_before: dateBefore,
@@ -257,7 +257,7 @@ export const DepositsList = (): JSX.Element => {
 				} >( {
 					path: getDepositsCSV( {
 						userEmail,
-						userLocale,
+						locale,
 						dateAfter,
 						dateBefore,
 						dateBetween,
diff --git a/client/deposits/list/test/index.tsx b/client/deposits/list/test/index.tsx
index 9698a50f899..5226853c564 100644
--- a/client/deposits/list/test/index.tsx
+++ b/client/deposits/list/test/index.tsx
@@ -90,9 +90,6 @@ declare const global: {
 			country: string;
 		};
 		dateFormat: string;
-		userLocale: {
-			code: string;
-		};
 	};
 };
 
@@ -160,9 +157,6 @@ describe( 'Deposits list', () => {
 				},
 			},
 			dateFormat: 'M j Y',
-			userLocale: {
-				code: 'en',
-			},
 		};
 	} );
 
@@ -375,7 +369,7 @@ describe( 'Deposits list', () => {
 				expect( mockApiFetch ).toHaveBeenCalledWith( {
 					method: 'POST',
 					path:
-						'/wc/v3/payments/deposits/download?user_email=mock%40example.com&locale=en',
+						'/wc/v3/payments/deposits/download?user_email=mock%40example.com&locale=en_US',
 				} );
 			} );
 		} );
diff --git a/client/disputes/index.tsx b/client/disputes/index.tsx
index 73837d8e865..1253a84efe3 100644
--- a/client/disputes/index.tsx
+++ b/client/disputes/index.tsx
@@ -351,7 +351,7 @@ export const DisputesList = (): JSX.Element => {
 		const { page, path, ...params } = getQuery();
 		const userEmail = wcpaySettings.currentUserEmail;
 
-		const userLocale = wcpaySettings.userLocale.code;
+		const locale = wcSettings.locale.userLocale;
 		const {
 			date_before: dateBefore,
 			date_after: dateAfter,
@@ -392,7 +392,7 @@ export const DisputesList = (): JSX.Element => {
 				} >( {
 					path: getDisputesCSV( {
 						userEmail,
-						userLocale,
+						locale,
 						dateAfter,
 						dateBefore,
 						dateBetween,
diff --git a/client/disputes/test/index.tsx b/client/disputes/test/index.tsx
index 2d20360426c..a0bc3f7a4b7 100644
--- a/client/disputes/test/index.tsx
+++ b/client/disputes/test/index.tsx
@@ -104,9 +104,6 @@ declare const global: {
 		};
 		dateFormat?: string;
 		timeFormat?: string;
-		userLocale: {
-			code: string;
-		};
 	};
 };
 
@@ -208,9 +205,6 @@ describe( 'Disputes list', () => {
 			},
 			dateFormat: 'Y-m-d',
 			timeFormat: 'g:iA',
-			userLocale: {
-				code: 'en',
-			},
 		};
 	} );
 
@@ -335,7 +329,7 @@ describe( 'Disputes list', () => {
 				expect( mockApiFetch ).toHaveBeenCalledWith( {
 					method: 'POST',
 					path:
-						'/wc/v3/payments/disputes/download?user_email=mock%40example.com&locale=en',
+						'/wc/v3/payments/disputes/download?user_email=mock%40example.com&locale=en_US',
 				} );
 			} );
 		} );
diff --git a/client/globals.d.ts b/client/globals.d.ts
index 0b61d866700..c721206e1bd 100644
--- a/client/globals.d.ts
+++ b/client/globals.d.ts
@@ -123,28 +123,6 @@ declare global {
 		isNextDepositNoticeDismissed: boolean;
 		isInstantDepositNoticeDismissed: boolean;
 		isConnectionSuccessModalDismissed: boolean;
-		userLocale: {
-			/**
-			 * The locale of the current user profile, represented as a locale code supported by transact-platform-server.
-			 *
-			 * @example 'es' // Spanish
-			 *
-			 * @see WC_Payments_Utils::convert_locale_to_language_code
-			 */
-			code: string;
-			/**
-			 * The English name of the locale.
-			 *
-			 * @example 'Spanish'
-			 */
-			english_name: string;
-			/**
-			 * The native name of the locale.
-			 *
-			 * @example 'Español'
-			 */
-			native_name: string;
-		};
 		trackingInfo?: {
 			hosting_provider: string;
 		};
diff --git a/client/transactions/list/index.tsx b/client/transactions/list/index.tsx
index 9d0be7a2196..63a69ff5464 100644
--- a/client/transactions/list/index.tsx
+++ b/client/transactions/list/index.tsx
@@ -591,8 +591,8 @@ export const TransactionsList = (
 		// eslint-disable-next-line @typescript-eslint/no-unused-vars
 		const { page, path, ...params } = getQuery();
 		const userEmail = wcpaySettings.currentUserEmail;
+		const locale = wcSettings.locale.userLocale;
 
-		const userLocale = wcpaySettings.userLocale.code;
 		const {
 			date_after: dateAfter,
 			date_before: dateBefore,
@@ -652,7 +652,6 @@ export const TransactionsList = (
 				await apiFetch( {
 					path: getTransactionsCSV( {
 						userEmail,
-						userLocale,
 						dateAfter,
 						dateBefore,
 						dateBetween,
@@ -673,6 +672,7 @@ export const TransactionsList = (
 						riskLevelIs,
 						riskLevelIsNot,
 						depositId,
+						locale,
 					} ),
 					method: 'POST',
 				} );
diff --git a/client/transactions/list/test/index.tsx b/client/transactions/list/test/index.tsx
index 5d4efbf827e..45f318f053a 100644
--- a/client/transactions/list/test/index.tsx
+++ b/client/transactions/list/test/index.tsx
@@ -111,9 +111,6 @@ declare const global: {
 				precision: number;
 			};
 		};
-		userLocale: {
-			code: string;
-		};
 	};
 };
 
@@ -258,9 +255,6 @@ describe( 'Transactions list', () => {
 					precision: 2,
 				},
 			},
-			userLocale: {
-				code: 'en',
-			},
 		};
 		window.wcpaySettings.dateFormat = 'M j, Y';
 		window.wcpaySettings.timeFormat = 'g:iA';
@@ -670,7 +664,7 @@ describe( 'Transactions list', () => {
 					method: 'POST',
 					path: `/wc/v3/payments/transactions/download?user_email=mock%40example.com&deposit_id=po_mock&user_timezone=${ encodeURIComponent(
 						getUserTimeZone()
-					) }&locale=en`,
+					) }&locale=en_US`,
 				} );
 			} );
 		} );
diff --git a/includes/admin/class-wc-payments-admin.php b/includes/admin/class-wc-payments-admin.php
index 5a1a6941682..9badfd47a8a 100644
--- a/includes/admin/class-wc-payments-admin.php
+++ b/includes/admin/class-wc-payments-admin.php
@@ -974,7 +974,6 @@ private function get_js_settings(): array {
 			'isInstantDepositNoticeDismissed'    => get_option( 'wcpay_instant_deposit_notice_dismissed', false ),
 			'dismissedDuplicateNotices'          => get_option( 'wcpay_duplicate_payment_method_notices_dismissed', [] ),
 			'isConnectionSuccessModalDismissed'  => get_option( 'wcpay_connection_success_modal_dismissed', false ),
-			'userLocale'                         => WC_Payments_Utils::get_language_data( get_user_locale() ), // Language code found in current user's profile. This is different from the site's locale.
 			'isOverviewSurveySubmitted'          => get_option( 'wcpay_survey_payment_overview_submitted', false ),
 			'trackingInfo'                       => $this->account->get_tracking_info(),
 			'lifetimeTPV'                        => $this->account->get_lifetime_total_payment_volume(),
diff --git a/includes/admin/class-wc-rest-payments-deposits-controller.php b/includes/admin/class-wc-rest-payments-deposits-controller.php
index 1b5c808a314..fb127a7eb04 100644
--- a/includes/admin/class-wc-rest-payments-deposits-controller.php
+++ b/includes/admin/class-wc-rest-payments-deposits-controller.php
@@ -132,11 +132,13 @@ public function get_deposit( $request ) {
 	 * @param WP_REST_Request $request Full data about the request.
 	 */
 	public function get_deposits_export( $request ) {
-		$user_email = $request->get_param( 'user_email' );
-		$locale     = $request->get_param( 'locale' );
-		$filters    = $this->get_deposits_filters( $request );
+		$user_email   = $request->get_param( 'user_email' );
+		$wpcom_locale = WC_Payments_Utils::convert_to_server_locale(
+			$request->get_param( 'locale' )
+		);
+		$filters      = $this->get_deposits_filters( $request );
 
-		return $this->forward_request( 'get_deposits_export', [ $filters, $user_email, $locale ] );
+		return $this->forward_request( 'get_deposits_export', [ $filters, $user_email, $wpcom_locale ] );
 	}
 
 	/**
diff --git a/includes/admin/class-wc-rest-payments-disputes-controller.php b/includes/admin/class-wc-rest-payments-disputes-controller.php
index 64e1e478a21..565e93c2ece 100644
--- a/includes/admin/class-wc-rest-payments-disputes-controller.php
+++ b/includes/admin/class-wc-rest-payments-disputes-controller.php
@@ -147,11 +147,13 @@ public function close_dispute( $request ) {
 	 * @param WP_REST_Request $request Full data about the request.
 	 */
 	public function get_disputes_export( $request ) {
-		$user_email = $request->get_param( 'user_email' );
-		$locale     = $request->get_param( 'locale' );
-		$filters    = $this->get_disputes_filters( $request );
+		$user_email   = $request->get_param( 'user_email' );
+		$wpcom_locale = WC_Payments_Utils::convert_to_server_locale(
+			$request->get_param( 'locale' )
+		);
+		$filters      = $this->get_disputes_filters( $request );
 
-		return $this->forward_request( 'get_disputes_export', [ $filters, $user_email, $locale ] );
+		return $this->forward_request( 'get_disputes_export', [ $filters, $user_email, $wpcom_locale ] );
 	}
 
 	/**
diff --git a/includes/admin/class-wc-rest-payments-transactions-controller.php b/includes/admin/class-wc-rest-payments-transactions-controller.php
index 9e7c10b76a4..a5cb55bac70 100644
--- a/includes/admin/class-wc-rest-payments-transactions-controller.php
+++ b/includes/admin/class-wc-rest-payments-transactions-controller.php
@@ -162,12 +162,14 @@ public function get_fraud_outcome_transactions_export( $request ) {
 	 * @param WP_REST_Request $request Full data about the request.
 	 */
 	public function get_transactions_export( $request ) {
-		$user_email = $request->get_param( 'user_email' );
-		$deposit_id = $request->get_param( 'deposit_id' );
-		$locale     = $request->get_param( 'locale' );
-		$filters    = $this->get_transactions_filters( $request );
+		$user_email   = $request->get_param( 'user_email' );
+		$deposit_id   = $request->get_param( 'deposit_id' );
+		$wpcom_locale = WC_Payments_Utils::convert_to_server_locale(
+			$request->get_param( 'locale' )
+		);
+		$filters      = $this->get_transactions_filters( $request );
 
-		return $this->forward_request( 'get_transactions_export', [ $filters, $user_email, $deposit_id, $locale ] );
+		return $this->forward_request( 'get_transactions_export', [ $filters, $user_email, $deposit_id, $wpcom_locale ] );
 	}
 
 	/**
diff --git a/includes/class-wc-payments-utils.php b/includes/class-wc-payments-utils.php
index 24608d2c898..16ea71292cd 100644
--- a/includes/class-wc-payments-utils.php
+++ b/includes/class-wc-payments-utils.php
@@ -1251,74 +1251,31 @@ public static function enqueue_style( $handle, $path = '', $deps = [], $version
 	}
 
 	/**
-	 * Returns language data: english name and native name
+	 * Converts a WP locale to a wpcom-compatible language code.
 	 *
-	 * @param string $language Language code.
+	 * @see Automattic\Jetpack\Jetpack_Mu_Wpcom\Common::get_iso_639_locale() for similar logic.
+	 * @see https://translate.wordpress.com/projects/wpcom/ for the current state of wpcom translations.
 	 *
-	 * @return array
-	 */
-	public static function get_language_data( $language ) {
-		require_once ABSPATH . 'wp-admin/includes/translation-install.php';
-
-		$translations = wp_get_available_translations();
-
-		if ( isset( $translations[ $language ] ) ) {
-			return [
-				'code'         => self::convert_to_server_locale( $language ),
-				'english_name' => $translations[ $language ]['english_name'] ?? $language,
-				'native_name'  => $translations[ $language ]['native_name'] ?? $language,
-			];
-		}
-
-		return [
-			'code'         => 'en_US',
-			'english_name' => 'English (United States)',
-			'native_name'  => 'English (United States)',
-		];
-	}
-
-	/**
-	 * Converts a locale to the server supported languages.
-	 *
-	 * @param string $locale The locale to convert.
-	 *
-	 * @return string Closest locale supported ('en' if NONE)
+	 * @param string $wp_locale a WordPress locale code to be converted e.g. "en_US", "pt_BR".
+	 * @return string language code compatible with wpcom e.g. "en", "pt-br".
 	 */
-	public static function convert_to_server_locale( string $locale ): string {
-		$supported = [
-			'ar',     // Arabic.
-			'de',     // German (Germany).
-			'es',     // Spanish (Spain).
-			'fr',     // French (France).
-			'he',     // Hebrew (Israel).
-			'id',     // Indonesian (Indonesia).
-			'it',     // Italian (Italy).
-			'ja',     // Japanese.
-			'ko',     // Korean.
-			'nl',     // Dutch (Netherlands).
-			'pt-br',  // Portuguese (Brazil).
-			'ru',     // Russian (Russia).
-			'sv',     // Swedish (Sweden).
-			'tr',     // Turkish (Turkey).
-			'zh-cn',  // Simplified, Singapore).
-			'zh-tw',  // Chinese Traditional (Taiwan).
-		];
-
-		// Replace '-' with '_' (used in WordPress).
-		$locale = str_replace( '_', '-', $locale );
-
-		if ( in_array( $locale, $supported, true ) ) {
-			return $locale;
-		}
-
-		// Remove the country code and try with that.
-		$base_locale = substr( $locale, 0, 2 );
-		if ( in_array( $base_locale, $supported, true ) ) {
-			return $base_locale;
+	public static function convert_to_server_locale( string $wp_locale ): string {
+		$wp_locale_lowercase                    = strtolower( $wp_locale );
+		$region_specific_wpcom_language_codes   = [ 'pt_br', 'pt-br', 'zh_tw', 'zh-tw', 'zh_cn', 'zh-cn' ];
+		$is_region_specific_wpcom_language_code = in_array( $wp_locale_lowercase, $region_specific_wpcom_language_codes, true );
+
+		$language_code = $is_region_specific_wpcom_language_code ?
+			// If it is a region-specific language code, we replace the underscore with a dash, e.g. 'pt_br' => 'pt-br'.
+			str_replace( '_', '-', $wp_locale_lowercase ) :
+			// Otherwise, we remove the country code and return only the language code, e.g. 'nl_NL' => 'nl'.
+			preg_replace( '/([-_].*)$/i', '', $wp_locale_lowercase );
+
+		if ( empty( $language_code ) ) {
+			// If the language code is empty, we return 'en' as a fallback.
+			return 'en';
 		}
 
-		// Return 'en_US' to match the default site language.
-		return 'en_US';
+		return $language_code;
 	}
 
 	/**
diff --git a/tests/js/jest-test-file-setup.js b/tests/js/jest-test-file-setup.js
index 09400abae27..59d98322955 100644
--- a/tests/js/jest-test-file-setup.js
+++ b/tests/js/jest-test-file-setup.js
@@ -75,7 +75,8 @@ global.wcSettings = {
 		failed: 'Failed',
 		paid: 'Paid',
 	},
-	l10n: {
+	locale: {
+		siteLocale: 'en_US',
 		userLocale: 'en_US',
 		weekdaysShort: [ 'Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat' ],
 	},
@@ -102,10 +103,6 @@ global.wpApiSettings = {
 };
 
 global.wcpaySettings = {
-	locale: {
-		code: 'es_ES',
-		native_name: 'Spanish',
-	},
 	accountLoans: {
 		loans: [ 'flxln_123456|active' ],
 	},
diff --git a/tests/unit/test-class-wc-payments-utils.php b/tests/unit/test-class-wc-payments-utils.php
index 61aa747fc00..25befd5eaf3 100644
--- a/tests/unit/test-class-wc-payments-utils.php
+++ b/tests/unit/test-class-wc-payments-utils.php
@@ -891,6 +891,37 @@ public function test_convert_to_stripe_locale() {
 		$this->assertEquals( 'es', $result );
 	}
 
+	/**
+	 * @dataProvider provider_convert_to_server_locale
+	 */
+	public function test_convert_to_server_locale( string $input_locale, string $expected_locale ) {
+		$result = WC_Payments_Utils::convert_to_server_locale( $input_locale );
+		$this->assertEquals( $expected_locale, $result );
+	}
+
+	public function provider_convert_to_server_locale(): array {
+		// Label => [ WordPress locale, transact-platform-server locale ].
+		return [
+			'Supported locale (Arabic)'                => [ 'ar_AR', 'ar' ],
+			'Supported locale (German)'                => [ 'de_DE', 'de' ],
+			'Supported locale (Spanish)'               => [ 'es_ES', 'es' ],
+			'Supported locale (French)'                => [ 'fr_FR', 'fr' ],
+			'Supported locale (Hebrew)'                => [ 'he_IL', 'he' ],
+			'Supported locale (Indonesian)'            => [ 'id_ID', 'id' ],
+			'Supported locale (Italian)'               => [ 'it_IT', 'it' ],
+			'Supported locale (Japanese)'              => [ 'ja_JP', 'ja' ],
+			'Supported locale (Korean)'                => [ 'ko_KR', 'ko' ],
+			'Supported locale (Dutch)'                 => [ 'nl_NL', 'nl' ],
+			'Supported locale (Portuguese (Brazil))'   => [ 'pt_BR', 'pt-br' ],
+			'Supported locale (Russian)'               => [ 'ru_RU', 'ru' ],
+			'Supported locale (Swedish)'               => [ 'sv_SE', 'sv' ],
+			'Supported locale (Turkish)'               => [ 'tr_TR', 'tr' ],
+			'Supported locale (Chinese (Simplified))'  => [ 'zh_CN', 'zh-cn' ],
+			'Supported locale (Chinese (Traditional))' => [ 'zh_TW', 'zh-tw' ],
+			'Empty locale fallback to en'              => [ '', 'en' ],
+		];
+	}
+
 	public function not_payment_settings_page_conditions_provider(): array {
 		return [
 			'is_admin() is false'                 => [ false, 'woocommerce_payments_foo', 'checkout' ],