How do I attached language specific css in Drupal 8? As the question states - how do I include a stylesheet based on a language? It has nothing to do with right to left reading, but for different colours etc.
You may want to use the "lang" attributes to style the language.

Here is the example:

&lt;!DOCTYPE html&gt;
&lt;html&gt;
&lt;head&gt;
&lt;style&gt;
p:lang(it) { 
    background: yellow;
}
&lt;/style&gt;
&lt;/head&gt;
&lt;body&gt;

&lt;p&gt;I live in Italy.&lt;/p&gt;
&lt;p lang="it"&gt;Ciao bella!&lt;/p&gt;

&lt;p&gt;&lt;b&gt;Note:&lt;/b&gt; For :lang to work in IE8, a DOCTYPE must be declared.&lt;/p&gt;

&lt;/body&gt;
&lt;/html&gt;