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Editorial Team
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Asked: 2026-06-14T14:22:32+00:00

Reading through the HTTP specification I came across the terms language-tag and language-range. The

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Reading through the HTTP specification I came across the terms “language-tag” and “language-range”. The standard defines the difference between these two entities as the following:

A language-range matches a language-tag if it exactly equals the tag, or if it exactly equals a prefix of the tag such that the first tag character following the prefix is "-".

However, the document doesn’t augment this statment by any of examples. So, how does the language-range differ from the language-tag in the following HTTP header field:

Accept-Language: en, en-gb, en-us

And if they don’t differ here, could you give any examples where they do.

Updated

I’d rephrase the aforementioned citation in the following manner:

A language is considered acceptable if its tag or the tag’s prefix exactly equals a language range which was specified in the Accept-Language field.

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  1. Editorial Team

    The RFC does provide an example. If you look at the specification of the Accept-Language request header:

    The Accept-Language request-header field is similar to Accept, but
    restricts the set of natural languages that are preferred as a
    response to the request. Language tags are defined in section 3.10.

      Accept-Language = "Accept-Language" ":"

                         1#( language-range [ ";" "q" "=" qvalue ] )

      language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )

    […]

      Accept-Language: da, en-gb;q=0.8, en;q=0.7

    […] "I prefer Danish, but will accept British English and
    other types of English."

    Section 3.10 mentions:

    The name space of language tags is administered by the IANA.

    So all language tags are registered here. Enter RFC 2616:

    A language-range (as used in an Accept-Language header) matches a language-tag if
    it exactly equals the tag, or if it exactly equals a prefix of the
    tag such that the first tag character following the prefix is "-".

    So, en in Accept-Language: en matches en-gb and en-US. If the client expects multiple matches for a single range, it should specify the subtags and assign a quality value (;q=) per subtag for best results.

    If it doesn’t, the server gets to decide which available representation it will return.

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