function icuMessageFormat(Prism) {
  // https://unicode-org.github.io/icu/userguide/format_parse/messages/
  // https://unicode-org.github.io/icu-docs/apidoc/released/icu4j/com/ibm/icu/text/MessageFormat.html
  ;(function (Prism) {
    /**
     * @param {string} source
     * @param {number} level
     * @returns {string}
     */
    function nested(source, level) {
      if (level <= 0) {
        return /[]/.source
      } else {
        return source.replace(/<SELF>/g, function () {
          return nested(source, level - 1)
        })
      }
    }
    var stringPattern = /'[{}:=,](?:[^']|'')*'(?!')/
    var escape = {
      pattern: /''/,
      greedy: true,
      alias: 'operator'
    }
    var string = {
      pattern: stringPattern,
      greedy: true,
      inside: {
        escape: escape
      }
    }
    var argumentSource = nested(
      /\{(?:[^{}']|'(?![{},'])|''|<STR>|<SELF>)*\}/.source.replace(
        /<STR>/g,
        function () {
          return stringPattern.source
        }
      ),
      8
    )
    var nestedMessage = {
      pattern: RegExp(argumentSource),
      inside: {
        message: {
          pattern: /^(\{)[\s\S]+(?=\}$)/,
          lookbehind: true,
          inside: null // see below
        },
        'message-delimiter': {
          pattern: /./,
          alias: 'punctuation'
        }
      }
    }
    Prism.languages['icu-message-format'] = {
      argument: {
        pattern: RegExp(argumentSource),
        greedy: true,
        inside: {
          content: {
            pattern: /^(\{)[\s\S]+(?=\}$)/,
            lookbehind: true,
            inside: {
              'argument-name': {
                pattern: /^(\s*)[^{}:=,\s]+/,
                lookbehind: true
              },
              'choice-style': {
                // https://unicode-org.github.io/icu-docs/apidoc/released/icu4c/classicu_1_1ChoiceFormat.html#details
                pattern: /^(\s*,\s*choice\s*,\s*)\S(?:[\s\S]*\S)?/,
                lookbehind: true,
                inside: {
                  punctuation: /\|/,
                  range: {
                    pattern: /^(\s*)[+-]?(?:\d+(?:\.\d*)?|\u221e)\s*[<#\u2264]/,
                    lookbehind: true,
                    inside: {
                      operator: /[<#\u2264]/,
                      number: /\S+/
                    }
                  },
                  rest: null // see below
                }
              },
              'plural-style': {
                // https://unicode-org.github.io/icu-docs/apidoc/released/icu4j/com/ibm/icu/text/PluralFormat.html#:~:text=Patterns%20and%20Their%20Interpretation
                pattern:
                  /^(\s*,\s*(?:plural|selectordinal)\s*,\s*)\S(?:[\s\S]*\S)?/,
                lookbehind: true,
                inside: {
                  offset: /^offset:\s*\d+/,
                  'nested-message': nestedMessage,
                  selector: {
                    pattern: /=\d+|[^{}:=,\s]+/,
                    inside: {
                      keyword: /^(?:few|many|one|other|two|zero)$/
                    }
                  }
                }
              },
              'select-style': {
                // https://unicode-org.github.io/icu-docs/apidoc/released/icu4j/com/ibm/icu/text/SelectFormat.html#:~:text=Patterns%20and%20Their%20Interpretation
                pattern: /^(\s*,\s*select\s*,\s*)\S(?:[\s\S]*\S)?/,
                lookbehind: true,
                inside: {
                  'nested-message': nestedMessage,
                  selector: {
                    pattern: /[^{}:=,\s]+/,
                    inside: {
                      keyword: /^other$/
                    }
                  }
                }
              },
              keyword: /\b(?:choice|plural|select|selectordinal)\b/,
              'arg-type': {
                pattern: /\b(?:date|duration|number|ordinal|spellout|time)\b/,
                alias: 'keyword'
              },
              'arg-skeleton': {
                pattern: /(,\s*)::[^{}:=,\s]+/,
                lookbehind: true
              },
              'arg-style': {
                pattern:
                  /(,\s*)(?:currency|full|integer|long|medium|percent|short)(?=\s*$)/,
                lookbehind: true
              },
              'arg-style-text': {
                pattern: RegExp(
                  /(^\s*,\s*(?=\S))/.source +
                    nested(/(?:[^{}']|'[^']*'|\{(?:<SELF>)?\})+/.source, 8) +
                    '$'
                ),
                lookbehind: true,
                alias: 'string'
              },
              punctuation: /,/
            }
          },
          'argument-delimiter': {
            pattern: /./,
            alias: 'operator'
          }
        }
      },
      escape: escape,
      string: string
    }
    nestedMessage.inside.message.inside = Prism.languages['icu-message-format']
    Prism.languages['icu-message-format'].argument.inside.content.inside[
      'choice-style'
    ].inside.rest = Prism.languages['icu-message-format']
  })(Prism)
}
Finds and tokenizes all template strings with an embedded languages.

@param {(Token | string)[]} tokens
@returns {void}