This thread is resolved. Here is a description of the problem and solution.
Problem: How to use same slugs for categories in all the languages
Solution: This is possible to have same slug for posts/pages. For the custom page/post to have the same slug, go to WPML=>Settings => Translated documents options=> and select "Translate (this will include the slug in the translation and not create it automatically from the title)"
but if it is a taxonomy/category/tags you can not do this. this is how WordPress was built. this is something should be fixed by WordPress. Not by WPML 🙂
Taxonomies can't be defined with the same slug in WordPress. If you try to create two taxonomy terms with the same slug in the same language WordPress will automatically add a numbered suffix at the end of them to make them unique.
Therefore WPML has been following that practice too. So while WordPress will add a number, WPML adds the language code to the slug.
With the actual versions you can't change to the same slugs from the WPML interface:
If you change a category slug from the WPML user interface, it will get a number (by WordPress) if you change it from the quick edit in WPML >Taxonomy translation it will get the language tag added.
But you can change it in the database if you really need it:
If you change it in the database by changing the slugs in the wp_terms table it will work correctly though. After changing the slug in the database you can also change it in the user interface of WPML > Taxonomy translation and it will keep there.
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