Localization parameter for back-end

Background

To translate messages it returns a back-end API needs to know the locale of the client.

Example message: "No item with barcode {itemBarcode} exists", for details see https://folio-org.atlassian.net/wiki/display/I18N/How+To+translate+FOLIO

Example locale: de for German

Two ways to pass the current locale to a back-end API have been proposed:

• accept-language HTTP header line
• lang query parameter

For details see FOLIO-3196 - Getting issue details... STATUS

While it may be possible that Stripes supports multiple ways to pass the locale FOLIO should agree upon a single way that all back-end modules should use.

This was discussed among front-end devs during multiple stripes-architecture meetings with conclusions in STRIPES-750 - Getting issue details... STATUS , and then by the Tech Council on 2021-06-09 and 2021-06-16.

Decision

• Back-end modules shall read the HTTP Accept-Language header, as specified in RFC-7231 Section 5.3.5, to determine the desired locale of the response.
  • The value is case insensitive (e.g. de and DE are equivalent).
  • Multiple values may be present in a comma-separated list.
    • Values may use weights in the range 0-1 appended to each value to indicate preference.
    • Values without a weight shall be considered 1.0.
    • Values with equal weights shall be considered to be ranked in descending order of preference.
    • e.g. de, en-gb;q=0.8, en;q=0.7
  • Values may optionally include subtags (e.g. de-DE). 
• The default value en-US will be used when a request lacks an Accept-Language header.
• Unspecified functionality should follow established precedent, e.g RFC-4646 (tags for identifying languages), RFC-7231 (HTTP Accept-Language header), ISO 639-1 (two-letter language codes), etc.