GlotPress interface indicates string priority order: high (↑), normal (no special marker), low (↓), and hidden (× – not shown for regular users).
When translating WordPress.com, it is best to translate strings in the order of priority. High priority strings are those that are associated with the new features or more visible elements of the interface, low priority strings are less visible/important, and hidden strings are generally not shown to regular WordPress.com users.
Hidden strings, however, are included in .po export files (it would be ideal to exclude them from export, but right now we don't have a way to do that automatically). Normally they are placed in the end of the file. So if you are a validator using an external tool like Poedit and then re-importing , make sure that you are translating the strings from the beginning of the file, rather than the end. We all want your translations to be visible and useful for as many users as possible!
I recently noticed a high number of hidden/low-priority strings for the following languages: Swedish, Thai, Turkish. Something to keep in mind, so that you spend your translation time most effectively.
As usual, thank you very much for your time and help translating, and if you have any questions or suggestions about GlotPress, string context, or translation best practices, don't hesitate to share them in this forum.