1. When literal translation is difficult or difficult for the target reader to understand.
2. When literal translation is not fluent or reading is not fluent.
3. When literal translation causes ambiguity
4. When literal translation loses the artistic conception of the original text.
5. When literal translation has no corresponding language.
6. When literal translation deviates from the original logic or meaning.
7. When literal translation can't rhyme, object or have format conflict.
8. When literal translation is inaccurate or inappropriate.
9. When literal translation cannot be realized.
10. When there are language and cultural conflicts in literal translation.
1- 10 free translation, otherwise literal translation.
As for what to add, what to make up, what to subtract, what to change, and how to adapt, we also follow the above principles, and vice versa (but in a certain priority).
The above is my opinion, for reference only.