Why is 寺 read differently in 長谷寺 and 平林寺?

Question

Both are proper nouns of temples; 長谷寺 is read as はせでら while 平林寺 is read as へいりんじ.

Is there any kind of rule to follow in order to know how to read the word?
Or is the reading arbitrary because both are proper nouns?

Answer 1

The reading for 長谷寺（はせでら）is 訓読み (くんよみ), which was derived from Japanese reading. 平林寺 (へいりんじ) is different in that it is 音読み (おんよみ), which was derived from the Chinese reading of Kanji.

Unfortunately, there is no definite rule for reading proper nouns.

In the case of temples, most readings tend to be 音読み. As Buddhism was introduced from China at around the 6th century, Buddhist scriptures at the time would be read in 呉音 (Wu-dynasty readings) or 漢音 (Han reading). Thus, it was natural for temples to be named using the Chinese readings.

To learn more, please see this article too: 清水寺は「せいすいじ」？ お寺の読み方、音訓混在の謎