gnome-terminal bengali unicode chars breaking, not showing perfectly

Question

In gnome-terminal, Bengali Unicode characters are showing, but not as should be shown. Vowels are not joining with consonants, such as "ব + া" should shown as "বা", but it is showing separately.

See screen-shot to clarify

Output for locale

LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=bn_BD.UTF-8
LC_TIME=bn_BD.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=bn_BD.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=bn_BD.UTF-8
LC_NAME=bn_BD.UTF-8
LC_ADDRESS=bn_BD.UTF-8
LC_TELEPHONE=bn_BD.UTF-8
LC_MEASUREMENT=bn_BD.UTF-8
LC_IDENTIFICATION=bn_BD.UTF-8
LC_ALL=