Health inequalities remain a major global health challenge [
1‐
3]. Particularly, migrants living in high-income countries and the general population of low- and middle-income countries (LMIC) are affected by a reduced availability of health services. This holds particularly true for mental health: although migrants often face various stressors before, during, and after migration [
4], it has been found that they are less likely to use mental health services and, if they use them, find them less helpful [
5,
6]. Similarly, a tremendous treatment gap in mental healthcare in LMIC has been revealed, i.e. the prevalence of mental disorders highly outnumbers the use of health services. It is estimated that, in LMIC, about 76–85% of people with a serious mental disorder do not receive any treatment, whereas about 35–50% receive no treatment in high-income countries [
7‐
9]. Reasons for these mental health inequalities are linked to structural as well as individual barriers. Structural barriers include a small number of available mental health services and a poor accessibility of existing services [
10‐
12]. Individual barriers include language and cultural barriers (e.g. understanding of disease and treatment processes, stigmatisation of mental disorders), a lack of information about the healthcare system, and a negative attitude towards the healthcare system [
10‐
13].
The World Health Organization has called to take action in order to adequately reach these specific populations that migrated from or live in LMIC and to hereby achieve an improved global health equality [
9]. This goal can only be reached when both individual and structural barriers are addressed. To reduce structural barriers, Internet- and mobile-based interventions (IMI) have been suggested as a low-threshold solution that enhances the accessibility of health services for a broad range of people in need [
13‐
20]. The advantages of IMI include their anonymity, temporal and local independence, easy accessibility, and scalability [
21‐
25]. The effectiveness of IMI has been proven in prevention, treatment, and aftercare for various mental disorders [
25‐
29]. However, IMI are mostly developed and evaluated for people living in high-income countries, and they seem to be less effective for people with a differing ethnic background [
30]. Thus, individual barriers to IMI have to be addressed simultaneously. Cultural adaptation of psychological interventions [
31‐
34], i.e. the consideration of “language, culture, and context in such a way that it is compatible with the client’s cultural patterns, meanings, and values” ( [
35]; p. 362), has been suggested to reduce existing individual barriers [
36,
37] and to enhance their acceptance, relevance, and effectiveness [
38‐
41]. Thus, culturally adapting IMI may be key to increase their reach and impact in culturally diverse people [
19,
42]. In fact, in recent years, various research groups have culturally adapted IMI for people with diverse cultural backgrounds [
43‐
47], which has been found to enhance the effectiveness of the IMI in the target groups [
48]. Most research groups hereby relied on frameworks for the cultural adaptation of face-to-face treatments [
31,
49‐
51], which, however, may not be valid when adapting IMI [
52]. Previous reviews and meta-analyses have summarised studies that conducted IMI in LMIC [
53] and investigated the extent and effectiveness of cultural adaptation of IMI for the treatment of common mental disorders among people with diverse cultural backgrounds [
48]. Yet, the procedure of the cultural adaptation is often only poorly reported [
43,
52,
54‐
56]. This makes it difficult to identify components of the cultural adaptation that may contribute to an enhanced acceptance and effectiveness of IMI, such as the language, illustrations, or example characters [
43,
54,
56,
57].
Furthermore, we will summarise the current evidence base on whether cultural adaptation of IMI for mental disorders leads to an increased acceptance, adherence, and effectiveness of such interventions.
Thus, this review will inform future researchers and developers working on the cultural adaptation of IMI for a mental disorder. The cultural adaptation of IMI holds great potential to reduce both individual and structural barriers to treatment-seeking, which might contribute to reduce global mental health inequalities.