Thanks Koen,
I had seen that page a long time ago, but it does not have the data I really want to have available for assessing the usefullness of translating a given plugin.
The most interesting stats pages I have seen are:
General plugin stats at https://moodle.org/plugins/stats.php (I try to keep 100% translated all the 20 most popular plugins)
and the individual plugin types stat pages, such as https://moodle.org/plugins/stats.php?plugin_category=29 for quiz question types.
I put the priorities that I think are worth taking into account at the documentation page in https://docs.moodle.org/dev/Translating_plugins#Plugin_translation_priority. Please feel free to change as you think is appropriatte.