[css-fonts-4] Copy the rest of Language-specific display from Level 3

Author: svgeesus

css-fonts-4/Overview.bs

@@ -2715,6 +2715,29 @@ to specific font features.
 <h3 id="language-specific-support">
 Language-specific display</h3>
 
+OpenType also supports language-specific glyph selection and
+positioning, so that text can be displayed correctly in cases where
+the language dictates a specific display behavior. Many languages
+share a common script, but the shape of certain letters can vary
+across those languages. For example, certain Cyrillic letters have
+different shapes in Russian text than in Bulgarian. In Latin text,
+it's common to render "fi" with an explicit fi-ligature that lacks a
+dot on the "i". However, in languages such as Turkish which uses both
+a dotted-i and a dotless-i, it's important to not use this ligature or
+use a specialized version that contains a dot over the "i".  The
+example below shows language-specific variations based on stylistic
+traditions found in Spanish, Italian and French orthography:
+
+<div class="featex"><img alt="language specific forms, spanish" src="images/locl-1.png"></div>
+<div class="featex"><img alt="language specific forms, italian" src="images/locl-2.png"></div>
+<div class="featex"><img alt="language specific forms, french" src="images/locl-3.png"></div>
+
+If the content language of the element is known according to the
+rules of the <a href="https://www.w3.org/TR/CSS21/conform.html#doclanguage">document language</a>,
+user agents are required to infer the OpenType language system from
+the content language and use that when selecting and positioning
+glyphs using an OpenType font.
+
 <!-- previously in level 3, now moved to Level 4 -->
 For OpenType fonts, in some cases it may be necessary to explicitly
 declare the OpenType language to be used, for example when displaying