The documentation seems to indicate not:
... You need to select the Translatable check box in Schemas if you want to allow these fields to be sent for translation...
However I was wondering if it there was some schema level setting to have all fields sent for translation by default. The use case is for a resource schema(s) containing translatable labels. From time to time new fields will be added for new resources, and its one more thing to remember to ensure they have the Translatable box checked.