If you are translating somebody else’s theme or plugin, you will want to make sure that future updates do not overwrite your own custom translation files.
The way to do this is ensure that your PO and MO files are saved in the global languages directory, and not inside the theme or plugin folder.
The global languages directory is at wp-content/languages, and the format for saved files is as follows:
Themes:
wp-content/languages/themes/<text-domain>-<locale>.mo
Plugins:
wp-content/languages/plugins/<text-domain>-<locale>.mo
Note that themes and plugins must be set up correctly for WordPress to load translations from the global folder.
You can also send the language files to me so I can include in them in future updates.
Thank you.