How to translate field groups and tabs, or strings that are not in the list of translatable strings?

Good evening everyone (or any other time of day)
Could you please help me? How can I translate strings that cannot be found in the translation list for the internalization, client, and translation table modules?
How do I translate such strings? For example, I can't translate tabs (it seems from the fieldgroup module), field groups...
Thank you in advance for your advice, answers, and other posts!