Language assessment is a central aspect not only of language education in the general population, but also amongst heterogeneous, low-incidence populations. One such population are immigrant deaf and hard-of-hearing learners (IDML) who are bimodal-multilingual and whose languages development often includes the spoken, written, and/or signed languages of the host country in addition to learners' home language(s) (Cannon and Marx 2024) ["Scoping review of research methodologies across language studies with deaf and hard-of-hearing multilingual learners." "International Review of Applied Linguistics in Language Teaching" 62 (2): 1009-1037]. Language assessment with these learners is complicated due to a lack of expected norms for the population and a lack of appropriate instruments for signed languages in general (Pizzo and Chilvers 2019) ["Assessment of Language and Literacy in Children Who Are d/Deaf and Hard of Hearing." "Education Sciences" 9 (3): 223]. This is a major issue for both research and pedagogy. In order to address this in the German context, a comparison of available assessment instruments focusing on vocabulary knowledge in written German and German Sign Language was carried out. The aim of this exploratory study was (1) to examine available language assessments, (2) to test them with a small sample representing the target population in order to determine their convergent validity, and (3) to provide recommendations for researchers and practitioners for their use. The results shed light on the potential for existing instruments to provide necessary and useful information for assessment in research and schools.