Language files can only be .dat

if (checkForTranslations) {
	string path = Path.Combine(directoryName, owner.language + ".dat");
	string path2 = Path.Combine(directoryName, "English.dat");
	if (File.Exists(path))
	{
		translationData = ReadFileWithoutHash(path);
		if (!owner.languageIsEnglish && File.Exists(path2))
		{
			fallbackTranslationData = ReadFileWithoutHash(path2);
		}
	}
	else if (File.Exists(path2))
	{
		translationData = ReadFileWithoutHash(path2);
	}
}

Sources:
AssetWorker.cs

#language