Would it be possible for translators/translation unions worldwide to enforce a unified minimum translation value such as $ 20 / 300 words?

Actually, in my own opinion i don't think that it would be  possible to do that or let's say it's going to be hard  to do so, for me  the price  doesn't matter if the    clients are satisfied.

I would simply say no because one cannot fix a minimum value especially for such a job. I mean, translators verily do vary, and so their experience, skill and thus should their value.