The study contributes to research on the development of the heritage language after return to the country of origin and examines whether the ultimate attainment of the heritage grammar after many years of residing in the country of origin brings returnees to a level compatible with that of monolinguals. We focus on the production and perception of evidentiality markers in the heritage Turkish of Turkish-German bilinguals who returned to Turkey after finishing a German high school and have been residing in Turkey for more than 11 years. Two production tasks (a narrative task and a discourse completion task), as well as a grammaticality judgement task were used in the study. The data analysis revealed that the production and perception of evidentiality by the returnee participants diverged from those of the monolingual control group. The divergence manifested itself in ungrammatical uses of evidentiality markers in the context of the indirect evidentiality and less sensitivity to grammatical and ungrammatical items comprising direct and indirect evidentiality markers. The findings of the study suggest that after many years of residing in Turkey the language behaviour of the returnee participants still possesses features that are typical for heritage speakers.

Aims and objectives/purpose/research questions: The aim of this study is to examine whether the complete (re-)activation of interface domains in the heritage language (HL) is possible or whether interfaces are likely to preserve features typical for the HL even after many years of residing in the country of origin. Design/methodology/approach: We present the group analysis of direct object marking in Turkish, which is a morphology-syntax-pragmatics interface, of Turkish-German returnees, who returned to Turkey after puberty and have been residing in the country for a minimum of 10 and a maximum of 34 years, and compare them with the control group consisting of Turkish speakers who have been living in Turkey all their lives. Data and analysis: The data were collected using a narrative task, a completion task and a grammaticality judgement task, and analysed both quantitatively and qualitatively. Findings/conclusions: The analysis of the narrative task revealed that the returnee participants used case-marking on direct objects productively depending on the discourse and syntactic position of the direct object in their heritage Turkish. However, their performance on the completion and grammaticality judgement tasks diverged from those of the control group. These findings can be considered as a piece of evidence that interface domains stay obstinate to complete (re-)activation and may preserve features typical for the HL many years after the return to the country of origin. Originality: The study suggests relevance of the Interface Hypothesis to the process of HL (re-)activation. Significance/implications: The study contributes to the research on the HL development of returnees after their return to the country of origin.