Is it socially/culturally acceptable for Indian/Sri Lankan people to visit the Oktoberfest?

Munich local here. We welcome everyone at Oktoberfest, doesn't matter where you're from or how you look.

The only things you really have to be careful about is getting excessively drunk (the beer is strong and plentiful), and getting into drunk arguments (which can get nasty when everyone has large, heavy glass steins in reach).

The Oktoberfest is a strongly German cultural event. It is for this reason that you are likely to be welcome there (rather than otherwise).

The Germans are looking to "spread the word" (regarding their culture) to people from other parts of the world. In this context, the fact that you are obviously "different" is a positive rather than a negative.

Just go there, have a good time, and makes sure that the Germans see that you are having a good time. It is friendly exchanges like this that help foster world peace.

(As a frame of reference, I was born to Asian parents and brought up by a German-American governess, so I have the view from both sides.)

Young Indian traveller's perspective here - every year many students (~700 - 1000+) from India's premier graduate and undergraduate colleges go on European student exchange semesters or internships around this time of year. I would say close to 60% of those students visit Oktoberfest, and I have seen Facebook feeds overflowing with Oktoberfest pics.

Apart from the students, there will be the occasional young globetrotting Indians from rich families as well.

Not a lot of those images are very publicly shared except outside closed groups, perhaps stemming from the way alcohol is generally seen in society here. But I can assure you people from the subcontinent do generally have a very good and memorable time at Oktoberfest.

To add to the other good answers: I am Bavarian, and in 2007 I attended the Esala Perahera in Kandy. It will be a similar experience when you visit the Oktoberfest. Some people might gaze at you out of curiosity for not looking like the majority. But over all, it is a celebration, and people are there for a good time (be it rooted in religion or not). This extends to all guests from elsewhere. So, yes, please do come and visit the Oktoberfest!

By the way: There are more Bavarian fests, that are similar in a way to the Oktoberfest, but smaller. Many Bavarians are more fond of those, since they are less crowded. If you have a chance to attend, e.g., the Regensburger Dult or the Gäubodenfest in Straubing, they are equally welcoming to guests from abroad.

Of course you're welcome. You don't even need to drink either. It's all pretty mellow and I've never heard of or seen any trouble. Just be aware of the cultural difference that some Germans, even when being what for them is considered relaxed and friendly, are still quite reserved. Some tents seem to be more corporate networking or hardcore drinking in closed groups (Stammtisch), not wanting to meet strangers. Just keep moving around until you find the friendly people. You might like to look beforehand on Meetup, Couchsurfing, Facebook etc. for group events you can join, or link up with other out-of-town visitors.

Not that you should need to, but if you want to get an extra-warm reception, wear a German (national-team) football shirt :-) or Alpine hat. They'll love that.

Tourists are absolutely welcome in Munich. The city is doing a lot to get tourists from all over the world to visit (and to bring money with them). Sales people from my company (close to Munich) bring customers from all over to the Oktoberfest every year and they love it.