How to specify translation for strings in twig template & php files I've found a lot of examples and modules where such expressions are used .

In php files 

 t('Submit this form'),


In twig files 

 {{ 'Send'|trans }}


So as I know this is used for the translation purpose, and I've also used these functions in my theme &amp; modules.

But the question is where I can specify translation for these words &amp; phrases ?
I think you could do that with the User interface translation, "/admin/config/regional/translate" (which is part of the multilingual core package).
By the way you can also use:

{% trans %} Your english text {% endtrans %}