In order for subscriptions to work on international catalogs, you must set localized values for subscription attributes (Subscription Mode, Frequency, Trial Days, Trial Product Code, and Trial Product Variation Code).
You will configure this translated content at the master catalog level in both System > Localization > Attributes and System > Localization > Attribute Values. For more information about these pages, see the product attributes guide.
The examples below show how subscription attributes might be translated for a master catalog that uses the fr-FR locale. The relevant attributes can be identified by the system~subscription prefix.