Support for rfc 5646

[jsamr]

Similarly to isISO8601, isRFC5646 will check if the given string param complies with the rfc 5646 standard for localisation tags (ex: fr-CA).

[chriso]

Happy to accept a PR 😄

[Haroenv]

How could this be done without having a complete list of languages in the library?

[profnandaa]

@jsamr - you can help here?

[jsamr]

@profnandaa Sorry don't have the time for this. Perhaps later this year.

[profnandaa]

No worries :)

On Tue, Sep 25, 2018 at 4:45 PM Jules Sam. Randolph < ***@***.***> wrote: @profnandaa <https://github.com/ProfNandaa> Sorry don't have the time for this. Perhaps later this year. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#572 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAP8kaxnxO3hdm3b58wCMYQjklSU8Mjcks5uejNtgaJpZM4JqX8e> .

-- Sent from a tiny device while on the move.

[lin826]

How could this be done without having a complete list of languages in the library?

Like the question from @Haroenv, we do need a complete list of IANA Language Tags.
Using their JS API might be a compromised solution.

I propose this:
Step 1. npm install their API, which has no string assertion.
Step 2. Add a file of isLanguageTag.js:

import tags from 'language-tags';

// Reference: https://tools.ietf.org/html/rfc5646
export default function isLanguageTag(str, options) {
    assertString(str);

    return tags.check(str)
}

Step 3. Add some tests from RFC 5646.

[Haroenv]

the project you linked still uses a full list of all languages, here: https://github.com/mattcg/language-subtag-registry