Using AMOS tool for language pack translation

Hi. I wanted to translate some new plugins, but I found one with 'translation stats not available'. https://moodle.org/plugins/mod_serlo/translations I could not see a string concatenation. So, I wonder what might be wrong with this plugin. I will greatley appreciatte if a programmer can teach me what is wrong with this plugin that prevents it from being available in AMOS. Thanks in advance.