Wikipedia
In linguistics, a semi-speaker is a speaker of an endangered language who has a partial linguistic competence in the language. Generally semi-speakers do not regularly use the endangered language in conversation, and their speech can contain erroneous forms. Semi-speakers are often among the most motivated and engaged participants in language revitalization projects.
As languages become obsolete and speech communities shift to other languages, they are spoken less frequently and in fewer social domains. Many speakers learn the language partially, often in a simplified way, with significant influence from the majority language. They are sometimes referred to as "semi-speakers", "quasi-speakers" or "rememberers". The word semi-speaker was introduced by linguist Nancy Dorian in describing the last speakers of the East Sutherland dialect of Scots Gaelic.
When semi-speakers form a significant part of the speech, community language contraction often ensues, as the linguistic norms are accommodated to the competences of the speakers.