If I want to add gtin feature, is it still translatable in the database? If yes, then it's problematic in case I've made a typo. Then I have to go through each language in order to fix it.
Could you add a special style for this kind of features e.g. gtin, maufacturer code, which should not be translatable?
For the time being, it's still translatable in the database. Ilya is aware of the issue, and a task already exists in the issue tracker. However, we'd rather avoid a rushed implementation in 4.10.1 and instead address the problem properly in one of the future versions.
There are at least 2 approaches: GTIN as a default field (as you initially suggested) or GTIN as a non-translatable feature (as I initially suggested). We would first need to decide which approach is better, and why.