Returns a locale for the specified IETF BCP 47 language tag string.

If the specified language tag contains any ill-formed subtags, the first such subtag and all following subtags are ignored. Compare to Locale.Builder.setLanguageTag which throws an exception in this case.

The following conversions are performed:

The language code "und" is mapped to language "".
The language codes "he", "yi", and "id" are mapped to "iw", "ji", and "in" respectively. (This is the same canonicalization that's done in Locale's constructors.)

The portion of a private use subtag prefixed by "lvariant", if any, is removed and appended to the variant field in the result locale (without case normalization). If it is then empty, the private use subtag is discarded:

     Locale loc;
     loc = Locale.forLanguageTag("en-US-x-lvariant-POSIX");
     loc.getVariant(); // returns "POSIX"
     loc.getExtension('x'); // returns null

     loc = Locale.forLanguageTag("de-POSIX-x-URP-lvariant-Abc-Def");
     loc.getVariant(); // returns "POSIX_Abc_Def"
     loc.getExtension('x'); // returns "urp"

When the languageTag argument contains an extlang subtag, the first such subtag is used as the language, and the primary language subtag and other extlang subtags are ignored:
```
     Locale.forLanguageTag("ar-aao").getLanguage(); // returns "aao"
     Locale.forLanguageTag("en-abc-def-us").toString(); // returns "abc_US"
 
```
Case is normalized except for variant tags, which are left unchanged. Language is normalized to lower case, script to title case, country to upper case, and extensions to lower case.

If, after processing, the locale would exactly match either ja_JP_JP or th_TH_TH with no extensions, the appropriate extensions are added as though the constructor had been called:

    Locale.forLanguageTag("ja-JP-x-lvariant-JP").toLanguageTag();
    // returns "ja-JP-u-ca-japanese-x-lvariant-JP"
    Locale.forLanguageTag("th-TH-x-lvariant-TH").toLanguageTag();
    // returns "th-TH-u-nu-thai-x-lvariant-TH"

This implements the 'Language-Tag' production of BCP47, and so supports grandfathered (regular and irregular) as well as private use language tags. Stand alone private use tags are represented as empty language and extension 'x-whatever', and grandfathered tags are converted to their canonical replacements where they exist.

Grandfathered tags with canonical replacements are as follows:

grandfathered tag modern replacement

art-lojban jbo

i-ami ami

i-bnn bnn

i-hak hak

i-klingon tlh

i-lux lb

i-navajo nv

i-pwn pwn

i-tao tao

i-tay tay

i-tsu tsu

no-bok nb

no-nyn nn

sgn-BE-FR sfb

sgn-BE-NL vgt

sgn-CH-DE sgg

zh-guoyu cmn

zh-hakka hak

zh-min-nan nan

zh-xiang hsn

grandfathered tag		modern replacement
art-lojban		jbo
i-ami		ami
i-bnn		bnn
i-hak		hak
i-klingon		tlh
i-lux		lb
i-navajo		nv
i-pwn		pwn
i-tao		tao
i-tay		tay
i-tsu		tsu
no-bok		nb
no-nyn		nn
sgn-BE-FR		sfb
sgn-BE-NL		vgt
sgn-CH-DE		sgg
zh-guoyu		cmn
zh-hakka		hak
zh-min-nan		nan
zh-xiang		hsn

Grandfathered tags with no modern replacement will be converted as follows:

grandfathered tag converts to

cel-gaulish xtg-x-cel-gaulish

en-GB-oed en-GB-x-oed

i-default en-x-i-default

i-enochian und-x-i-enochian

i-mingo see-x-i-mingo

zh-min nan-x-zh-min

grandfathered tag		converts to
cel-gaulish		xtg-x-cel-gaulish
en-GB-oed		en-GB-x-oed
i-default		en-x-i-default
i-enochian		und-x-i-enochian
i-mingo		see-x-i-mingo
zh-min		nan-x-zh-min

For a list of all grandfathered tags, see the IANA Language Subtag Registry (search for "Type: grandfathered").

Note: there is no guarantee that toLanguageTag and forLanguageTag will round-trip.

Parameters:

languageTag the language tag

Returns: The locale that best represents the language tag.

Exceptions:

NullPointerException if languageTag is null

Since: 1.7