As far as I can see here (https://pkp.sfu.ca/wiki/index.php?title=Translating_OxS#OJS_Languages) there is no support for Latvian for the time being.
Is there a possibility to add support for a new language manually? Because we publish articles in various Central and Eastern European languages and one of these is in Latvian we just wanted to highlight that the article is in Latvian (we don’t need all of the webpages in Latvian). In other words, we would just want that when the author chooses the language of his or her submission s/he can click “Latvian”. We don’t need support for Latvian in the sense that all the forms, etc. are available in Latvian.