Your LimeSurvey version: 5.4.2+220921 (Limesurvey Community Edition)
Own server or LimeSurvey hosting: Universitat de València
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I am designing a survey in Spain and I would like to add more languages to the survey so that we can translate the survey into Galician, Euskera, Catalan and English. Nevertheless, when I try to select new languages, there are only a few available (for example, English, Catalan, German, Turkish...) but I cannot manually add Galician or Euskera to the survey.

For us, it is very important to be able to have our survey in those 5 languages (Galician, Euskera, Catalan, English and Spanish). Is there any possibility we can manually add Galician and Euskera to our survey? 

Thank you. 

In your Global Settings "Configuration / Global / Languages":
Are these languages "visible" or "hidden"
 
As you see here in my installation ALL languages are visible.
And I can select all these languages in my survey.
 
  

But you use an installation of your university. Maybe you have no access to this setting.
Ask the admin.

Joffm

 

I see Galican in the translation status list but not Euskera.

- translate.limesurvey.org/projects/limesurvey-4/

You may need to create a new language.

- www.limesurvey.org/manual/Translating_LimeSurvey

I think "Euskara" is the same as "Basque".
 

I think "Euskara" is the same as "Basque".

Joffm is correct. Basque is the English name for Euskera.

My educated guess: The super admin has not allowed Euskera/Basque and Gallego as a language in this installation. You would need to speak to the person responsible for Limesurvey at the University of Valencia.

Also keep in mind the translation status of certain languages:

English: 100%
Catalan: 99%
Spanish (Spain): 97%
Galician: 75%
Euskera/Basque: 41%

The missing translation might appear in English. Many of these untranslated strings might be actually translated but not approved / fuzzy in the system (see the list here, it says LS4 but it is actually for LS5 as well: translate.limesurvey.org/projects/limesurvey-4/ ).

Many of the untranslated strings might just be for the backend, so this is usually no big issue. But there might be certain error messages, etc. that might not be translated and might appear in the questionnaire.