Added a new language (Catalan) to the game's localization, since the base game is fully translated to it, I figured I could translate this mod as well. :)
I made a PR on the project repository: https://github.com/MagmaMcFry/Factorissimo2/pull/54

Some automatic cleanup has happened (removed duplicates, keys not found in english, end of lines, etc.), since I've used this tool to localize it:
https://github.com/dima74/factorio-mods-localization

Which shows the localizations here:
https://crowdin.com/project/factorio-mods-localization

New localizations of the mod can be added through the crowdin page, but they will get autocommitted to my fork, not the main repo, which would be ideal. :)

If you're interested on getting localizations from crowdin without having to accept PRs, the only issue is that the tool expects the files to have the same names between languages, so they cannot be called "/en/en-factory" and "/ca/ca-factory", but "/en/factory.cfg" and "/ca/factory.cfg".

Thank you! I've integrated your PR. Does Crowdin at least know that "en.cfg" and "ca.cfg" are supposed to be the same file?

Great!
No, crowdin needs them to be all the same name or it won't relate them.
I had to fix before using crowdin and un-fix it before uploading the PR (it's just a second, but it's not good for source control).

The ideal scenario is for mods to not use the name of the language on the cfg files, but the name of what is being covered on each locale file. If there's only 1 file on a mod, I'd say locale.cfg or base.cfg is perfectly fine to use.

Alright, I'll do that. Thanks for the heads-up!

Let me know if you need any assistance on this.

Once you unified the names of the localization files, you will probably need to add and remove the repository from the github app here: https://github.com/apps/factorio-mods-localization-helper

Please note that the option of selecting all repositories from github is yet not supported, so you will need to manually select each repository you want to translate. :)