That's great! If you have made a modification to a mod and want to make it clear that you do not own the original rights to the mod, it's a good idea to include a disclaimer or notice in the description or documentation of your modified version. This way, you make it clear to users that they should refer to the original mod creator for support or issues related to the mod itself.
As for the Welsh version you mentioned, it's fantastic that you have created a localized version of the mod. Providing different language versions can help make mods accessible to a wider audience. If you want to share the Welsh version, consider uploading it to a mod hosting platform or a website where other players can download it and enjoy the content in their preferred language. Remember to adhere to any licensing terms that the original mod creator has set for their work.