Ruthenian language

Regional distribution of those varieties, both in their literary and vernacular forms, corresponded approximately to the territories of the modern states of Belarus and Ukraine.

By the end of the 18th century, they gradually diverged into regional variants, which subsequently developed into the modern Belarusian, Ukrainian, and Rusyn languages, all of which are mutually intelligible.

[33][a] He identified the Polissian (Polesian) dialect spoken on both sides of the modern Belarusian–Ukrainian border as the basis of both written Ruthenian (rusьkij jazykъ or Chancery Slavonic) and spoken dialects of Ruthenian (проста(я) мова prosta(ja) mova or "simple speech"),[34] which he called 'two stylistically differentiated varieties of one secular vernacular standard'.

[38] The vernacular Ruthenian "business speech" (Ukrainian: ділове мовлення, romanized: dilove movlennya) of the 16th century would spread to most other domains of everyday communication in the 17th century, with an influx of words, expressions and style from Polish and other European languages, while the usage of Church Slavonic became more restricted to the affairs of religion, the church, hagiography, and some forms of art and science.

[39] The 1569 Union of Lublin establishing the Polish–Lithuanian Commonwealth had significant linguistic implications: the Crown of the Kingdom of Poland (which now included Ukraine) had previously used Latin for administration, but switched to Middle Polish (standardised c. 1569–1648[40]), while the Grand Duchy of Lithuania (including Belarus, but no longer Ukraine) gave up Chancery Slavonic (Ruthenian) and also switched to Middle Polish.