Complex sentence: This end, he conducted published and unpublished research in Tsakonian and other outlier Greek dialects, which present interesting problems in such analysis, and this gave him a broad familiarity with the whole body of research on Tsakonian, including Deffner's work.
Split into simpler sentences: This end, he conducted published and unpublished research in Tsakonian and other outlier Greek dialects, which present interesting problems in such analysis. This gave him a broad familiarity with the whole body of research on Tsakonian, including Deffner's work.