Please tell me how to make duplicate custom field names?
For example, a custom Size field for the category Children's Clothing and Size (title) for the category Clothing for Men.
Ie the name Size (custom field) for 2 different categories.
Now I can not display - I write that such a name already exists

may be custom fields enhancer plugin helps you, check it, there is a video available.

I just have this plugin Custom Field Enhancer, but this still does not change anything
Do not Tell me how to do it or watch a video how it can be done?

You can try to add extra language and add in custom fields eg. - Item, Item1, Item2, Item3...., then translate these custom fields.
You need to modify core for translating custom fields, this you can find in osclass forum.

I did not try in such way, but this is some idea, if success, let know.

Thanks for the answer - I'll try and accomplish this