@ollehar, @gabrieljenik, could you check why the translation was added but is not yet available for selection? Usually that is just 3-4 lines missing at one of the helper files, if I remmeber correctly.

Never had to deal with such a situation... Maybe better for @ollehar ? Sorry

@ollehar, can you have a short look why the translation is available at the translation tool but not yet selectable within Limesurvey?
Usually it is just adding 3-4 lines at the helper file with the language definitions.

@c_schmitz any idea? Or maybe @DenisChenu

It is a bit of an egg-and-hen problem. We don't add translation languages where we don't have any translations yet.
I probably set up the language because someone asked for it, but also told that person that some translations have to be done first, before it is being pushed into a release.
Apparently, that person never translated anything, so it never made it into a release version.

@c_schmitz, thanks a lot for the clarification.

WHO may provide some translations for Yoruba. Could we add the language to LS 3.x and 5.x/6.x?

Yes, same applies here. Some translations need to be done first. Yoruba is currenty available on translate.limesurvey.org for all versions.
Just look for the strings that frontend would use, then translate these. After at least 20 strings are translated notify me and I will push it to release.