The initial implementation of suggestions (T106405) does not provide options to change the languages suggestions are provided for.
We should allow users to select the languages they want for their suggestions:

• Allow to select any language. Users should be able to select any language pair and get suggestions for it. Note that this should only apply to the suggestions view. For the rest of the views (in progress, and published) it makes sense to act as usual (filtering the languages used in translations and with a generic "any languages" by default).
• Facilitate selection of usual languages. The ULS language selector should be provided including a "Common languages" section that provides quick access to the usual user languages (languages used for translating as well as the usual criteria based on browser, location and previous selections).
• Prevent from selecting the same language as both source and target. Users should not be able to select "English > English". To prevent that, we can use a "swap" strategy as it is done in the new translation dialog: If the initial selection is "A>B", and the user modifies "B" to be "A", the resulting selection will be "B>A". That not only prevents the issue but also allows users to easily reverse the translation direction (i.e., changing from "English>Hindi" to "Hindi > English" in one go).
• Use smart defaults. Especially for first time users we may not have previous language choices info. We can start by a simply using the current wiki language as target language and make a best chance choice based on our stats for source (e.g., English if it is not the target).