Restore Alsace-Lorraine! is a decision for France. It requires, that a German state have annexed Alsace-Lorraine and taken the decision Reichsland Elsaß-Lothringen to rename the province to its German name.
When France takes back the province, it is possible to restore the old name. It also gives 10 prestige.
The decision can be taken multiple times if Germany have conquered the province and renamed it to Elsaß-Lothringen more than once.