Language translations are done on a volunteer basis, so the quality and even installation instructions may vary. The standard installation instructions are in the Storeowner Docs > Admin Pages > Localization > Languages.
You are always welcome to help improve a translation, by either making your suggestions known to the author of the translation or by making your wanted changes yourself.
The handling of language files was re-architected in Zen Cart 1.5.8 to deal with new PHP 8 behavior. Documents in this folder refer to Zen Cart 1.5.8 and above. If you need information on how older versions worked, please see Pre 1.5.8 Language Files.