Let users pick both base and target languages when translating

[aabounegm]

When editing a translation, the selected story translation is implicitly selected as the target translation and the user gets to pick the base against which to compare. This confuses the users who do not thoroughly read the prompt and therefore assume they are picking the translation to edit rather than the one to use for comparison.
The easy way around this is to open a dialog prompting both base and target languages (could even be pre-filled with the target) to make the choices explicit and clear.