user24: Sakurasou no Pet na Kanojo is an LN with a recent anime adaptation. The tag sakurasou-no-pet-na-kanojo is 26 characters, which just barely doesn't fit, so the user who created it here used sakurasou-no-pet instead. This is a reasonable choice, but not necessarily the best one. There is an English name, "The Pet Girl of Sakurasou", which would fit at 25 characters if we used the-pet-girl-of-sakurasou. Personally I've not heard the English title used much. 
What tag should we use for this series?

user247: Why not simply use sakurasou and note its full name in the description? Alternatives can be added as synonyms.

user1528: The english tag name the-pet-girl-of-sakurasou works as it is valid, legible and is nested within SE's tag naming restrictions so I say use it instead.
On your comment about the popularity of the english title, "sakurasou" is present in both so it should be found quite easily.

24: <p><a href="http://en.wikipedia.org/wiki/The_Pet_Girl_of_Sakurasou" rel="nofollow noreferrer">Sakurasou no Pet na Kanojo</a> is an LN with a recent anime adaptation. The tag <a href="https://anime.stackexchange.com/questions/tagged/sakurasou-no-pet-na-kanojo" class="post-tag" title="show questions tagged &#39;sakurasou-no-pet-na-kanojo&#39;" rel="tag">sakurasou-no-pet-na-kanojo</a> is 26 characters, which just barely doesn't fit, so the user who created it <a href="https://anime.stackexchange.com/questions/4482/why-is-maid-chan-voice-actor-listed-as-in-ending-credits">here</a> used <a href="https://anime.stackexchange.com/questions/tagged/sakurasou-no-pet" class="post-tag" title="show questions tagged &#39;sakurasou-no-pet&#39;" rel="tag">sakurasou-no-pet</a> instead. This is a reasonable choice, but not necessarily the best one. There is an English name, "The Pet Girl of Sakurasou", which would fit at 25 characters if we used <a href="https://anime.stackexchange.com/questions/tagged/the-pet-girl-of-sakurasou" class="post-tag" title="show questions tagged &#39;the-pet-girl-of-sakurasou&#39;" rel="tag">the-pet-girl-of-sakurasou</a>. Personally I've not heard the English title used much. </p>

<p><strong>What tag should we use for this series?</strong></p>
 247: <p>Why not simply use <a href="https://anime.stackexchange.com/questions/tagged/sakurasou" class="post-tag" title="show questions tagged &#39;sakurasou&#39;" rel="tag">sakurasou</a> and note its full name in the description? Alternatives can be added as synonyms.</p>
 1528: <p>The english tag name <a href="https://anime.stackexchange.com/questions/tagged/the-pet-girl-of-sakurasou" class="post-tag" title="show questions tagged &#39;the-pet-girl-of-sakurasou&#39;" rel="tag">the-pet-girl-of-sakurasou</a> works as it is valid, legible and is nested within SE's tag naming restrictions so I say use it instead.</p>

<p>On your comment about the popularity of the english title, "sakurasou" is present in both so it should be found quite easily.</p>
