@Mapper(uses = TranslationMapper.class)
public interface PrimaryClassMapper {
    @Mapping(source = "primary.id", target = "id")
    @Mapping(
            source = "primary.translatedNames",
            target = "name",
            qualifiedByName = {"TranslationMapper", "TranslationsToString"})
    SecondaryClass toSecondaryClass(PrimaryClass primary, @Context Language targetLanguage);
}

@Named("TranslationMapper")
public class TranslationMapper {
    @Named("TranslationsToString")
    public String resolveTranslatedText(
            List<TranslationDto> translations, @Context Language targetLanguage) {
        //some fancy logic
    }
}