Whether through SimPE or another program, I would really appreciate the help. Thank you very much too!

I'm going to assume you have at least some experience with SimPE and modding.

Most mods are easy to translate, but it can take some time. You'll have to translate pie menus, ingame catalog descriptions, regular dialogs, popup dialogs, and/or chance cards - it depends on what kind of mod you are making.

Usually you need to translate these if the mod has them:
-Catalog Description
-Pie Menu Strings
-Text Lists (with popup dialog), common names for these could be:
--->Dialog prim string set
--->MakeActionString prim string set
(Text lists are used for a lot of things, you don't have to translate all of them. You'll most likely recognize the correct ones based on the mod you're translating)

When you click on one of these, you find a dropdown box with languages in the regular Plugin View window. Choose the language you want to add from that list, and start to write in the "String" box. Make sure you fill all the boxes that have numbers under the #, and that you check with the main language (usually English), so everything is translated correctly. When you're done with that language, click "commit" (if you take a break or want to check something elsewhere in the file, click "commit" before clicking a different resource and also before saving, because changes aren't properly saved unless you click "commit"). Save the file when you're done (and at points where you don't want to lose progress).

Added pictures below (they're numbered 1 to 3, but the uploader apparently can't count properly today ), to show buttons and all that, and did a really bad translation of something that probably didn't need one, just to show how.

PS: The list of trees shown in the pictures wasn't something that needed translation, and really shouldn't have been translated at all, but it was the shortest and easiest list I found in the mod I used for the example pics, so I just picked it to show the how-to.

Just to add to that, you generally shouldn't translate text lists other than the ones mentioned above, because that could cause things to break. These text lists may not be named, you should identify them using the Type and Instance Number in SimPE. Catalog strings are always of type CTSS, and pie menu strings are of type TTAs, anything with those types is proper to translate. For Type STR#, you should only translate Instance 0x12D (Dialog strings) and Instance 0x12E (MakeAction strings). I don't think there are any STR# Type resources that should be translated.

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You have helped me how you can not imagine, the written explanation confused me a bit at the beginning, but by rereading it calmly, I managed to understand perfectly. I thank you for taking the time to put pictures, because it helped me to reinforce the explanation. Thank you, seriously!

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I'll take it into account so as not to spoil anything, it is truly useful information. Thank you!