settings: For subtitle of selected language, repeat canonical self-name

It looks odd to have an item with:

title: 简体中文（中国）
subtitle: 中文（中国）

That's "Chinese (China)", where the first one is the canonical
self-name and the second is the name chosen by our volunteer
translators.

Better to have:

title: 简体中文（中国）
subtitle: 简体中文（中国）

The canonical self-name is what we've chosen for consistency with
other globally minded organizations, like Wikipedia.

(We could instead just omit the subtitle, but if we did, then all
the rows in the list would have two lines of text except the
selected row which would have just one. And that non-uniformity
might look odd.)

src/settings/SettingsScreen.js

@@ -135,7 +135,7 @@ export default function SettingsScreen(props: Props): Node {
         items={languages.map(l => ({
           key: l.tag,
           title: noTranslation(l.selfname),
-          subtitle: l.name,
+          subtitle: l.tag === language ? noTranslation(l.selfname) : l.name,
         }))}
         onValueChange={value => {
           dispatch(setGlobalSettings({ language: value }));