I often see people here reasoning about what sounds colloquial to them and what doesn't which has its implications on the decision of someone who's asking for help.
Who defines what is colloquial and what isn't?
Is there an authority that maintains the Russian language standard?
As far as I know, there is no de facto authority over the language. The Institute of Russian Language is just a research institution.
Update: As pointed out by @Kira, in the federal law #53-ФЗ has been passed in 2005. It states that the Russian Goverment may decide on the precedure to define norms and rules of the modern language for use as a state language (1.3. Порядок утверждения норм современного русского литературного языка при его использовании в качестве государственного языка Российской Федерации, правил русской орфографии и пунктуации определяется Правительством Российской Федерации). In 2006, the Goverment has issued a decree #714, and made the Ministry of Education and Science responsible for creating a list of officially approved dictionaries, grammar compendia, and rules of orthography and punctuation. As of today I cannot find any trace of existence of such a list. Probably it is not ready yet. Even if this list exists, it doesn't cover all the other uses of the language (like personal and business communication, literature, spoken language etc.).
So there is (still) no single language standard.
While there is no single standard, there are many academically recognized publications, which we deem authoritative. Their authors are usually groups of well-known linguists. Newer publications are to be preferred, particularly if you want to learn about modern use of a word.
To learn if a word is colloqial or not, you may just check the dictionary. Many of them are available online. Consider using
Colloquial words tend to be labeled as разг. (разговорное, spoken), жарг. (жаргон, slang), or прост. (просторечное, uneducated). Sometimes colloquial words become mainstream, so prefer newer dictionaries to judge.
There are also free state-supported services which can answer questions about the language:
As from my experience and knowledge, there is institution, which regulates standarts of the Russian language. The rules of the Russian literary language are established by the Russian government.
Here is quotation from the federal state #53:"Порядок утверждения норм современного русского литературного языка при его использовании в качестве государственного языка Российской Федерации, правил русской орфографии и пунктуации определяется Правительством Российской Федерации."
Surely the government asks for assistance groups of linguists, historians of the Russian language, etc.
If the new rule appear, it'll appear first of all in Mass Media, then the corrections will be applied in new dictionaries.
It is absolutely informal matter. It's only about culture, education, good breeding, informal norms and rules shared by society.
