What are the language codes standards for internationalization purposes?

The ISO Codes for the Representation of Names of Languages although used for websites is actually insufficient for software internationalization purposes, since it doesn't distinguish between variants of the same language, such as Portuguese of Portugal and Brazilian Portuguese.

Some programming languages and operative systems solve this problem by adding a suffix to specify the variants (pt_PT and pt_BR respectively).

But are there any standardization efforts to solve this problem?

Some languages as you may know also support Locale variants, for example Norwegian Nynorsk or Norwegian Bokmal (as no_NO_NY and no_NO respectively).

Windows OS supports the concept of LCID which contains Language, Sub-Language, sorting options, etc.

Now, onto your question: is there any standardization effort in this area?
To be honest, I have never heard of one. That of course doesn't mean that nobody is working on it. However, I believe that both language identifiers ISO631 and ISO3166 exist for reasons not related to information exchange via computers. These codes were needed in foreign trade and I am quite confident that this is the reason they were created.
Please take into account that Locale representation is not standardized, you would see something like en_US, en-US and 1033 for the same thing. If we want to create some sort of standard, we need to think about it first, then as an extension standardize variants. I don't think it will happen very soon if ever...

Wikipedia lists a couple of language codes. The pt_BR format is an IETF language tag.

You might like ISO-639-3 better. No one liked -2.