Trégorrois Breton is the dialect of Breton spoken in Trégor (Bro-Dreger in Breton).
Distinguishing characteristics
Trégorrois differs from other varieties of the language in a number of ways:
It always uses the possessivehon (often pronounced hom) whereas the other dialects use hol before l, hon before n,d,t,h and vowels, and hor before all others (these other forms are nonetheless understood because of exposure to hymns and songs, for instance)
After the possessive hon, Trégorrois makes a sibilant variation (e.g., where Vannetais uses /hon tu/, or Cornouaillais and Léonard hon ti, Trégorrois says hon zi)
Different from Léonard, z is generally not pronounced (nor is it in Cornouaillais and Vannetais)
The tonic accent is very strong (for example, bihan is pronounced /b:in/)
Certain constructions are preferred. For instance, me a wel ac'hanout or plijet on ouzh da welout instead of plijet on o welout ac'hanout
Frequently the 'd' will not mutate into a z where it would in the other dialects (for example, ar paotr a dañs)
The glyphw is generally pronounced ou (e.g., war is pronounced /uar/), unlike Léonard dialect where it is pronounced /v/
There are several other pronunciation details. For example, an heol is pronounced /ãn heul/ (compare to the /ar mur/ of Kemper). This is possible in Trégorrois because the very strong aspiration of /h/ avoids any confusion with the word 'oil' (eoul).
Finally, future endings are different. The future of Middle Breton was -homp, -het, -hont. Trégorrois moved from h to f (forms in -fomp, -fet, -font, etc.). (Compare with the forms -ahomp, -ahet,-ahont of Vannetais, due to the appearance of an -a- elision (pronounced /e/).
Source
This article is based on the French-language Wikipedia's article: Breton trégorrois.