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Very likely this is because your OS or your Browser is in English, test on another machine, which is with local language Pt that should appear in msg in Portuguese.
Other than that you can try to force a language change in the document’s HTTP header, or by declaring lang on the tag html or with the goal http-equiv in the content hers.
<!DOCTYPE html>
<html lang="pt-br"><!-- recomendado pela W3C -->
<head>
<meta http-equiv="content-language" content="pt-br"><!-- não recomendado pela W3C -->
<meta charset="utf-8" />
<title>Page Title</title>
</head>
<body>
</body>
</html>
To Mozilla makes no reservations as to meta http-equiv, already the W3C does not recommend.
W3C recommends that you declare directly in the HTTP header the Content-Language: pt-br or on the tag html
This use of
content-languagevalue of ahttp-equivattribute is disapproved by the HTML specification and should no longer be used. Instead, you should always use alangattribute inhtmltag to declare the default language of the text on the page.

Vide MDN Form data validation - Customized error messages: "They Depend on the browser locale, which Means that you can have a page in one language but an error message displayed in Another language."
– Woss