So far, unusable because it only reads keys.
It insists on translating the keys, not the values. For example, the xliff has the key "app.description.3" with an English value of "This app is a great game for all ages". The POEditor only allows translating the key "app.description.3" which is machine code, not human readable language.

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If your project terms are string IDs, you should set a Default Reference Language on the project, in Project Settings, as described here: https://poeditor.com/kb/setting-a-default-reference-language
If you want to use the Automatic Translation feature, just make sure you choose as translation source one of languages in the project, and not the project terms: https://poeditor.com/kb/using-the-automatic-translation-feature