The .oxt files in this repository are Open Office extension files that provide spell checking and hyphenation dictionaries compatible with the hunspell library used in the viewer. The canonical repository for the .oxt files is at: http://extensions.services.openoffice.org/en/dictionaries
They have been manually downloaded here so that they can be easily packaged into the viewer installer. Before adding any additional dictionaries, ensure that the licenses are compatible with inclusion in the Linden Lab (commercial) viewer.
TODO: add a URL to a wiki page on how to download and install dictionaries.