Non-translatable strings are automatically marked in your localization projects when you import terms with a
translatable="false" flag from an Android XML file.
As this flag is specific to Android XML, it is not possible to set it manually or using any other localization file format.
When you import the non-translatable strings to the source language in your POEditor project, the source language needs to be set as Default Reference Language, otherwise the non-translatable values will be ignored.
After you import the untranslatable values in your Default Reference Language, they will be copied in all your other project languages and locked, so that they can't be edited.
Note: To update a non-translatable string, make a new translations import using an updated Android XML file in the Default Reference Language, and check the box to overwrite old translations.