The on-screen texts of XnView are the texts that you read in the user interface of XnView. For each language, one translators is assigned. Sometimes, a translator does not find the time anymore. Then, a new translator is wanted, you will see a post in this group, then.
Currently, XnView supports about 40 languages. Usually, when there is a new release of XnView, new labels are added which need to be translated. Sometimes translators are informed late about a new version and cannot translate in time, the result is an XnView version with some few non-translated labels. Typically, the translation is updated in the next minor release, then.