Some general guidelines on what to watch out for and ask about:
Chinese: Watch out for chicken broth (even in “vegetable” dishes),
eggs (often in soups, egg roll wrappers, lo mein noodles. Ask for egg left
out of veggie fried rice and moo shu).
Ethiopian: Most vegetarian dishes are usually vegan, but dairy
is occasionally used (usually in the form of butter or a fresh, soft cheese).
Indian/Nepalese: There are usually many vegetarian options,
just beware of dairy which can pop up in many forms, especially paneer
(cheese), ghee (clarified butter), yogurt, and cream (in many sauces, breads,
chutneys, drinks, and even rice sometimes).
Italian: Most dried pastas are vegan, however restaurants which
make their own pastas tend to use egg in the dough. Some tomato sauces
may contain animal broth or dairy products (cheese), most marinaras are
okay, though. Olive oil and garlic is a good alternative if you find yourself
stuck. Likewise a lot of dried gnocci is vegan, but most fresh made gnocci
are not.
Japanese: Ask about fish sauce or bonito (fish flakes). These
can show up in everything from seaweed salad to miso soup and beyond. You
can usually at least get some vegan sushi rolls (maki), and an udon (wheat
noodle dish) or two at a sushi restaurant .
Mexican: Watch for chicken stock in rice, lard in beans and
tortillas, and dairy (sometimes sour cream is used) in guacamole. Plus
ask to leave off the cheese/sour cream where listed, obviously.
Middle Eastern: Usually felafel, hummus, tabouleh, fattoush,
muhammara (walnut spread with red pepper and/ or pomegranate) and pita
are okay. Baba ganoush and tahini sauces may or may not be dairy-free (some
contain yogurt). Tzaziki contains yogurt.
Thai: Look out for egg (especially in pad thai and other noodle
dishes and rice dishes) and fish sauce (nam pla) or shrimp paste in curries
and other items.
Vietnamese: Watch out for eggs and especially fish sauce which
can be used widely and may not be listed on menus. Even dishes listed as
“vegetarian” may typically come with fish products, as the word is
understood differently culturally.