System language change functionality

[Will-LWE]

Hello,

I offer this small contribution to allow changing the system language from the bios settings which is always in English after each start of the emulation.

With this modification, it is now possible to change the language from the "-l" or "--language" command line, then the option can also be modified from the application settings and then saved in the configuration file.

Some games, like Rayman for example, do not allow you to select the language and are based on the language configuration from the system settings. This can be annoying if a player wants to play their game in their native language or of their choice.

Test performed on Linux. The code can be changed if necessary. Tests may be necessary on other platforms to confirm the correct functioning of this new functionality.

The code is added for Retro Arena, Libretro, SDL and NX but must be tested.

Hoping that this contribution can interest you because it brings a comfort during the game to the player.

[Will-LWE]

Hello,
I have corrected the integration of language on Libretro. I tested on Raspberry Pi and It works fine.