Techniques (in research) ; Research techniques ; Coordinate bilingualism; Compound bilingualism; Dominanz (biling.) ; Dominance (biling.) ; Continuum (biling.) ; Multilingualism; Polylingualism; Plurilingualism ; Cross-linguistic influence (psycholing.) ; Language loss (biling.) ; Attrition (biling.) ; Language attrition (biling.) ; Auswanderer; Emigrants; Migrant; Aussiedler; Gastarbeiter; Arbeitsmigranten; Immigrants/Emigrants ; Transfer (languages in contact) ; Adstratum language; Adstratsprache; Interference ; Sprachbewahrung; Ethnolinguistic vitality; Vitality, ethnolinguistic; Sprachwechsel; Language shift; Heritage language; Language maintenance ; Transfer (second language acquisition) ; Transfer (Zweitspracherwerb) ; Cross-linguistic influence (second language acquisition) ; Interference (second language acquisition) ; Critical period (second language acquisition) ; Alter (Einfluss auf Zweitspracherwerb) ; Age (influence on second language acquisition) ; Ultimate attainment (second language acquisition) ; Near-native competence (second language acquisition) ; AoA; Age of acquisition (second language acquisition) ; Sensitive period (second language acquisition) ; Interference (morph.) ; Phonische Interferenz; Languages in contact (phon.) ; Sprachkontakt (phon.) ; Interference (phon.) ; Interference (synt.)