how to apply more font families

[ershat-dl]

I am one of the flutter beginners. so I have been studing flutter-folio, and I think it is very nice for me.
but I have a idea , and can not figure out.
first take a look at flutter-folio's code.

class Fonts {
  static const String raleway = "Raleway";
  static const String fraunces = "Fraunces";
}

/// TextStyles - All the core text styles for the app should be declared here.
/// Don't try and create every variant in existence here, just the high level ones.
/// More specific variants can be created on the fly using `style.copyWith()`
/// `newStyle = TextStyles.body1.copyWith(lineHeight: 2, color: Colors.red)`
class TextStyles {
  /// Declare a base style for each Family
  static const TextStyle raleway = const TextStyle(fontFamily: Fonts.raleway, fontWeight: FontWeight.w400, height: 1);
  static const TextStyle fraunces = const TextStyle(fontFamily: Fonts.fraunces, fontWeight: FontWeight.w400, height: 1);

static TextStyle get h1 =>
      inter.copyWith(fontWeight: FontWeight.w600, fontSize: FontSizes.s48, letterSpacing: -1, height: 1.17);

  static TextStyle get h2 => h1.copyWith(fontSize: FontSizes.s24, letterSpacing: -.5, height: 1.16);
...
}

in this code, now I have two fonts, one is English font, another one is Japanese font.
When App Started, in Material app 's builder method,and I checked current locale language code.
if it is en, then copy themeData with english font, else it is jp, then copy with japanese font. and then return themeData.
now , I want to use TextStyles.h2 with english font, like 'raleway' when app locale is english,
and I want to use TextStyles.h2 with japanese font, too, like 'xxx' when app locale is japanese,
now problem is, when I using TextStyles.h2, its fontFamily property is raleway.
how could I improve this ?

so guys, could you give me some guides about this , thanks