Translate non-dynamic strings with Poedit
This documentation should help you translate non-dynamic strings. A non-dynamic string is a string that you can't change from the customizer. Here is an example on the Blog page of Hestia Pro.
In this example, we will use Hestia Pro and we'll try to translate those strings in Romanian. Please make sure that your site is displayed in the desired language.
In order to translate these strings, you need to install a program like Poedit.
First step after you have Poedit installed is to look at the theme files and find the .pot file. For example, in Hestia Pro, you will find it in /languages/hestia-pro.pot
Open the hestia-pro.pot file with Poedit.
Now you have to generate .po and .mo files for each language that you want to translate your site. I will generate them for Romanian.
Click File->Save as and name the file with this format depending on the language code of 2 letters. For Romanian is ro_RO and for English is en_EN. You can check the WP Locale code here. Make sure to save the .po file in the theme files languages directory.
Now you should have the both .po and .mo files for the desired language in theme files languages directory.
Now you will work only with the .po file. Open the .po file for desired language using Poedit. In this case it is ro_RO.po file.
Here you have to search for the desired string and in the bottom panel of Poedit you can write the translation for it.
After you wrote all the translations save the .po file.
Now those strings should be translated on the site.
If you are using Polylang and the strings don't appear properly please take a look at this documentation on How to add a language switcher to the menu.