R1:2b41ed01c692

Fix no-op transaction error on `paste.create` Conduit API method

Summary:
Fixes T9735. I changed how the TYPE_LANGUAGE transction works a little but that accidentally tripped an error condition in `paste.create`.

- Don't bail on no-effect transactions to `paste.create` (like not setting a language).
- When a transaction type has no tailored UI message, make it easier to figure out which transaction is problematic.

Test Plan: Ran `arc paste ...` locally. Got an error before the patch, clean paste…