Rightnow, in games use GetAvailableLanguageCodes(), there is a WriteBuffer() with size larger than the buffer_size. (Core Critical core\hle\kernel\hle_ipc.cpp:WriteBuffer:296: size (0000000000000088) is greater than buffer_size (0000000000000078))

0x88 = 17(languages) * 8
0x78 = 15(languages) * 8

GetAvailableLanguageCodes() can only support 15 languages.
After firmware 4.0.0 there are 17 supported language instead of 15, to enable this GetAvailableLanguageCodes2() need to be used.
So GetAvailableLanguageCodes() will be caped at 15 languages.
Reference:
http://switchbrew.org/index.php/Settings_services