<p>This paragraph is English, but the language is not specifically defined.</p>

<p lang="en-GB">This paragraph is defined as British English.</p>

<p lang="fr">Ce paragraphe est défini en français.</p>

p::before {
  padding-right: 5px;
}

[lang='en-GB']::before {
  content: '(In British English) ';
}

[lang='fr']::before {
  content: '(In French) ';
}