Steps to repeat:
1. Set up a site with base (English) and one other language (Swedish for example)
2. Visit admin/config/regional/translate/translate and search for
- String contains: "" (empty)
- Language: "Swedish"
- Search in: "Only untranslated strings"
- Limit search to: "Built-in interface"
I expect to receive a list of strings that haven't been translated into Swedish.
"No strings available."
I wanted to keep the steps to repeat fairly short, so here goes a longer description.
I'm assuming that my expectation is correct - the "Language" filter is meant to filter on target language, and in combination with the "Search in" filter we should be able to find either strings that have been translated into that language, or strings that haven't been translated into that language.
The way it currently works, the "Only untranslated strings" filter will only return strings when paired with the "English" or "All languages" settings for the Language filter. And in that case it will return "all strings that haven't been translated into any language". Which doesn't seem like a reasonable use case to me. Thus bug.