These questions are not really sentences. This one could be reworded as "How is Xfce installed?" The next ones:
How is Xfce Started?
What about localization?
How can unified themes be used with GTK3 and GTK2?
How can xfdashboard be launched at startup?
How can keyboard shortcuts be changed for programs like Thunar and xfce4-terminal?
How is compositing enabled?
How can menu items be hidden?
How can the panel be hidden with fullscreen applications?
How can PulseAudio be disabled?

Typo: s/wiht/with/

<strong> is probably not needed.

No comma needed.

Either "to use the pkg(8) utility" or just "to use pkg(8):".

Please avoid using "you" and "your". Instead:

<p>To use Xdm, apply this <a

Please avoid contractions:

It is a well-known bug (<a

(Should this be "It fixes a well-known bug"?)

Please avoid using "you":

Even if the system has already been <a href="../doc/en_US.ISO8859-1/books/handbook/l10n.html">configure​d for localization</a>, additional localization settings must be added to <tt>.xinitrc</tt> file.</p>

"that" is not needed, just "defined like:"

No comma after encoding, and "define a new variable,".

the value of the

Try to avoid asides:

Or make sure the <tt>autostart/</tt> directory exists, and copy the <tt>xfdashboard-autostart.desktop</tt> file into it.

To avoid "you":

Keyboard shortcuts can now be defined.

When the item menu is active (highlighted), keyboard shortcuts can be directly defined by passing the mouse over it.

the <strong>Compositor</strong>

the value

No need for the aside:

and right-click on one item in the right pane, then select...

Sometimes when applications are in full-screen mode, panels are

Avoid "you":

The value of <tt>disable-struts</tt> can be changed.

Either "the file" or just remove "file"

In <tt>~/.config/pulse/client.conf</tt>, replace these lines:

themes instead of 'thems'.

I'd use "How can we adopt the same behavior as ...".

Add the "the" here as well, and also use behavior (without u) for consistency. ;-)

I think it sounds better to use:
By default, Thunar displays ...

"the" same ...

s/new/a new/

Sorry, I didn't see this before: should that be "called"?

address -> addressed

environments -> environment

hightlighted -> highlighted

settings -> setting (only one)

Duplicating several existing entities here seems like it could cause problems in the future when the originals change. It should be possible to include the existing URL entities. (I can make suggestions on that later.)

These two forum entities are only used once in the text and might as well be a literal link.

This is only used once, so does not seem to need the overhead of making it an entity.

If possible, add to existing url entities and import them. If not, at least use the same naming conventions, for url.xfce.

These two Gnome entities are only used once in the text. Might as well be a literal link.