Hello Wensolutions,
many thanks for your answers. We have already followed the steps mentioned in the link https://wptravel.io/translation-of-the-strings/ but unfortunally with no success!
We translated it this way (I hope you can see the screenshot):
ScreenShot1
and we get this:
ScreenShot2
so we tried to edit the file wp-travel-utilities-es_ES.po by hand to get the translation inside the “…” but unfortunately this did not solve the problem.

Finally, since we urgently needed the translation in Spanish, we have directly modified the “functions.php” file, but this can only be a temporary solution …
ScreenShot3
Could you please investigate this problem? We probably miss some steps…

Regards.
Elena