Argos Translate (argosopentech/argos-translate) is an open source offline translation library written in Python. The repository was created in April 2020, and its most recent release is v1.4.0. Installing .argosmodel language packages that hold the data required for translation lets you translate locally without an internet connection. Model packages are downloaded and installed separately for each language pair.
The README states that this library uses OpenNMT, which is used for neural machine translation, and that it can be used as a Python library and a command-line tool. It also ships a graphical user interface (GUI) application. Language pairs without a direct translation model can be handled by pivot translation through an intermediate language. The license is MIT, and the repository has 6,584 stars. LibreTranslate is an API and web app built on this library.
Still, some points remain unclear. What changed in v1.4.0 is not written down in the collected sources. There are no benchmarks comparing translation quality either, and no figures are given for how much accuracy shifts under pivot translation. The language pairs that actually work are exactly what the installed .argosmodel packages define. The rating has only a momentum score of 3.1, with no freshness, technology, or quality items. So it is hard to draw a firm conclusion about the effect of adopting it until the supported languages and the release change log are checked directly.