Hi @CarlosMoreira70 ,
Could you please share a bit more about your scenario?
Do you want to display a default Calendar name within the Dropdown box based on the user's local language?
Based on the issue that you mentioned, I think the Language function could achieve your needs. I have made a test on my side, please take a try with the following workaround:

Set the Items property fo the Dropdown box to following:
DropColumns(
AddColumns(
Office365.CalendarGetTables().value,
"CalendarName",
If(
DisplayName = "Calendar",
If( /* <-- Based on user's locale, display corresponding Calendar name value */
Right(Language(),2) = "US",
"Calendar",
Right(Language(),2) = "FR",
"Calendrier",
Right(Language(),2) = "DE",
"Kalender"
),
DisplayName = "Birthdays",
If(
Right(Language(),2) = "US",
"Birthdays",
Right(Language(),2) = "FR",
"Anniversaires",
Right(Language(),2) = "DE",
"Geburtstage"
),
DisplayName = "United States holidays",
If(
Right(Language(),2) = "US",
"United States holidays",
Right(Language(),2) = "FR",
"Vacances aux Etats-Unis",
Right(Language(),2) = "DE",
"USA Feiertage"
)
)
),
"DisplayName"
)
Then set the Default property of the Dropdown box to following:
If(
Right(Language(),2) = "US",
"Calendar",
Right(Language(),2) = "FR",
"Calendrier",
Right(Language(),2) = "DE",
"Kalender"
)
More details about the Language function in PowerApps, please check the following article:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-language
If you want to reference the Calendar Id from above Dropdown box (to create events), please consider use the following formula:
Dropdown1.Selected.Name /* <-- returns the Calendar Id for the selected Calendar name e.g. AAMkAGNlZWJhNDFhLWVkZDQtNGEwMi1hNGYxLWE4NjgxODQxYjE1OABGAAAAAADs9uoqJJanQrMetqhMVhx6BwCSaWLzoY45Rr_4uGphA-0GAAAAAAEGAACSaWLzoY45Rr_4uGphA-0GAAIdUAygAAA=*/
Best regards,