> Skt.: _viha:ra_ 'temple'
> Pali: _viha:ra_ 'temple'
> Malay: _biara_ 'monastery'
> Thai: _phiha:n_ "biha:ra" 'temple'
> Thai: _wiha:n_ "wiha:ra" 'shrine, abbey'
(etc)
The change of Skt /v/ to modern /b/ is regional. It is found in Hindi,
Eastern Rajasthani, Kumauni, Nepali, the Bihari group, Bengali, Oriya and
Assamese, but not found in Marathi, Gujarati, Sindhi, Kashmiri. Very
roughly, it is found in the central-eastern area.
So one thought that leaps to mind is that Thai forms with /#w-/ are either
from dialects that retained /#w-/, or else direct borrowings from Skt at a
later date, giving a doublet in Thai. Worldwide, such doublets are
commonplace.
Peter