Microsoftalexheer It might be intentional.
en-au, en-ca, en-ie, en-in, en-my, en-nz, en-sg, en-za, en-zw all use the en-GB language.
Below is the language mapping done in the new Teams which is part of the fallback-map.json file:
{
"az-az": "az-latn-az",
"be-by": "ru-ru",
"de-at": "de-de",
"en-029": "en-us",
"en-bz": "en-us",
"de-ch": "de-de",
"de-li": "de-de",
"de-lu": "de-de",
"en-au": "en-gb",
"en-ca": "en-gb",
"en-ie": "en-gb",
"en-in": "en-gb",
"en-my": "en-gb",
"en-nz": "en-gb",
"en-sg": "en-gb",
"en-ph": "en-us",
"en-tt": "en-us",
"en-za": "en-gb",
"en-zw": "en-gb",
"es-419": "es-es",
"es-ar": "es-mx",
"es-bo": "es-mx",
"es-cl": "es-mx",
"es-co": "es-mx",
"es-cr": "es-mx",
"es-do": "es-mx",
"es-ec": "es-mx",
"es-gt": "es-mx",
"es-hn": "es-mx",
"es-ni": "es-mx",
"es-pa": "es-mx",
"es-pe": "es-mx",
"es-pr": "es-mx",
"es-py": "es-mx",
"es-sv": "es-mx",
"es-us": "es-mx",
"es-uy": "es-mx",
"es-ve": "es-mx",
"fr-be": "fr-fr",
"fr-ch": "fr-fr",
"fr-lu": "fr-fr",
"fr-mc": "fr-fr",
"it-ch": "it-it",
"ky-kg": "ru-ru",
"lb-lu": "de-de",
"nl-be": "nl-nl",
"qut-gt": "es-es",
"quz-pe": "es-es",
"sr-cyrl": "sr-latn-rs",
"sr-cyrl-rs": "sr-latn-rs",
"sr-latn": "sr-latn-rs",
"sr-rs": "sr-latn-rs",
"sv-fi": "sv-se",
"tg-cyrl-tj": "ru-ru",
"tk-tm": "ru-ru",
"tt-ru": "ru-ru",
"ug-cn": "zh-cn",
"wo-sn": "fr-fr",
"zh-hans": "zh-cn",
"zh-hans-cn": "zh-cn",
"zh-hans-sg": "zh-cn",
"zh-hant": "zh-tw",
"zh-hant-hk": "zh-tw",
"zh-hant-mo": "zh-tw",
"zh-hant-tw": "zh-tw",
"zh-hk": "zh-tw",
"zh-mo": "zh-tw",
"zh-sg": "zh-cn",
"ar": "ar-sa",
"az": "az-latn-az",
"bg": "bg-bg",
"ca": "ca-es",
"cs": "cs-cz",
"cy": "cy-gb",
"da": "da-dk",
"de": "de-de",
"el": "el-gr",
"en": "en-us",
"es": "es-es",
"et": "et-ee",
"eu": "eu-es",
"fi": "fi-fi",
"fil": "fil-ph",
"fr": "fr-fr",
"gl": "gl-es",
"he": "he-il",
"hi": "hi-in",
"hr": "hr-hr",
"hu": "hu-hu",
"id": "id-id",
"is": "is-is",
"it": "it-it",
"ja": "ja-jp",
"ka": "ka-ge",
"ko": "ko-kr",
"kk": "kk-kz",
"lt": "lt-lt",
"lv": "lv-lv",
"mk": "mk-mk",
"nb": "nb-no",
"nl": "nl-nl",
"nn": "nn-no",
"pl": "pl-pl",
"pt": "pt-br",
"ro": "ro-ro",
"ru": "ru-ru",
"sk": "sk-sk",
"sl": "sl-si",
"sr": "sr-latn-rs",
"sq": "sq-al",
"sv": "sv-se",
"th": "th-th",
"tr": "tr-tr",
"uk": "uk-ua",
"vi": "vi-vn",
"zh": "en-us",
"de-de": "de-de",
"el-gr": "el-gr",
"en-gb": "en-gb",
"en-us": "en-us",
"es-es": "es-es",
"es-mx": "es-mx",
"et-ee": "et-ee",
"eu-es": "eu-es",
"fi-fi": "fi-fi",
"fil-ph": "fil-ph",
"fr-ca": "fr-ca",
"fr-fr": "fr-fr",
"gl-es": "gl-es",
"he-il": "he-il",
"hi-in": "hi-in",
"hr-hr": "hr-hr",
"hu-hu": "hu-hu",
"id-id": "id-id",
"is-is": "is-is",
"it-it": "it-it",
"ja-jp": "ja-jp",
"ka-ge": "ka-ge",
"kk-kz": "kk-kz",
"ko-kr": "ko-kr",
"lt-lt": "lt-lt",
"lv-lv": "lv-lv",
"mk-mk": "mk-mk",
"nb-no": "nb-no",
"nl-nl": "nl-nl",
"nn-no": "nn-no",
"pl-pl": "pl-pl",
"pt-br": "pt-br",
"pt-pt": "pt-pt",
"ro-ro": "ro-ro",
"ru-ru": "ru-ru",
"sk-sk": "sk-sk",
"sl-si": "sl-si",
"sq-al": "sq-al",
"sr-latn-rs": "sr-latn-rs",
"sv-se": "sv-se",
"th-th": "th-th",
"tr-tr": "tr-tr",
"uk-ua": "uk-ua",
"vi-vn": "vi-vn",
"zh-cn": "zh-cn",
"zh-tw": "zh-tw"
}