У меня вот такие вопросы: 1) Какие изоглоссы объединяют английский с фризскими? 2) Какие уникальные фичи отделяют английский от прочих западногерманских языков?
1) A-fronting: WGmc a, ā → æ, ǣ, even in the diphthongs ai and au (see Anglo-Frisian brightening)
palatalization of Proto-Germanic *k and *g before front vowels (but not phonemicization of palatals)
A-restoration: æ, ǣ → a, ā under the influence of neighboring consonants
Second fronting: OE dialects (except West Saxon) and Frisian ǣ → ē
A-restoration: a restored before a back vowel in the following syllable (later in the Southumbrian dialects); Frisian æu → au → Old Frisian ā/a
OE breaking; in West Saxon palatal diphthongization follows
i-mutation followed by syncope; Old Frisian breaking follows
Phonemicization of palatals and assibilation, followed by second fronting in parts of West Mercia
Smoothing and back mutation
https://en.wikipedia.org/wiki/Anglo-Frisian_languages2) Diphthongisation of long and short front vowels in certain positions ("breaking").
Loss of certain weak vowels in word-final and medial positions, and of medial [(i)j]; reduction of remaining unstressed vowels.
Diphthongisation of certain vowels before certain consonants when preceding a back vowel ("back mutation").
Loss of /h/ between vowels or between a voiced consonant and a vowel, with lengthening of the preceding vowel.
Collapse of two consecutive vowels into a single vowel.
"Palatal umlaut", which has given forms such as six (compare German sechs).
https://en.wikipedia.org/wiki/Old_English#History