Content Translation supports URL campaigns to provide direct access to the tool to translate a specific article. For example: https://en.wikipedia.org/wiki/Special:ContentTranslation?campaign=wiki-for-human-rights&page=Universal+Declaration+of+Human+Rights&from=en&to=tl

Currently, for this to work the target language ("to" parameter) is mandatory. However, in some cases, external tools may want to provide a link for users to translate one particular article to any language without specifying one in particular. That is, by using a link such as https://en.wikipedia.org/wiki/Special:ContentTranslation?campaign=wiki-for-human-rights&page=Universal+Declaration+of+Human+Rights&from=en

When the target language is not set explicitly, it can be automatically selected as it is done for translations that are started from the translation dashboard (based on an automatic guess based on previous translations, selected languages, browser settings, etc.).

An alternative could be to force the user to make an explicit choice for the target language in such cases, but that would require further consideration base on how frequently users are lead to a translation to the wrong language, since an initial guess, even when wrong, does not add extra effort from the user compared to having no selection.