I observed once how the Japanese name “咲良” was rendered into Hangul as “사쿠라,” instead of its equivalent pronunciation in Hanja (which according to Google Translate is something like “소량”). Is this always the case? Or does it change depending on the source language, like Mandarin?
First off: TL; DR.
Transliterations are preferred. Well-known on’yomi音読み names are sometimes read with Hanja sounds.
Foreign words in the Korean language
By the standard of the NIKL, you should transliterate foreign names and words into Hangul, preserving their original pronunciations — with some exceptions.
Some on’yomi音読み (“음독音讀” in Korean) toponyms and terminology can also be read with Korean Hanja sounds. You don’t do that to kun’yomi訓読み (“훈독訓讀” in Korean) words, which is why you don’t read “咲良Sakura” as “소량.”
- “東京Tōkyō” → “동경” (or the transliteration “도쿄”)
- “北海道Hokkaidō” → “북해도北海道” (or the transliteration “홋카이도”)
- “対馬Tsushima” → “대마對馬도島 island” (or the transliteration “쓰시마Tsushima섬island”)
- “幕府bakufu” → “막부幕府” (This is more like an imported word, though — in that it is seldom read as the transliteration “바쿠후.”)
Taiwanese and Chinese words
As kun’yomi訓読み doesn’t play in here, more words are read with Korean Hanja sounds.
- “南京Nánjīng” → “남경” (or the transliteration “난징”)
- “北京Běijīng” → “북경” (or the transliteration “베이징”)
- “上海Shànghǎi” → “상해” (or the transliteration “상하이”)
- “广东Gwong2 Dung1” → “광동廣東” (or the transliteration “광둥”)
- “臺灣[tʰäɪ˧˥ ʋän˦]” → “대만” (or the transliteration “타이완”)
Some personal names
- “毛 泽东Máo Zédōng” → “모택동毛澤東” (or the transliteration “마오쩌둥”)
- and the names of people lived before the Xinhai revolution (the establishment of the Republic of China)
Some landmark names
- “天安门Tiān’ānmén” → “천안문天安門” (or the transliteration “톈안먼”)
Some song titles
- “月亮代表我的心Yuèliang Dàibiǎo Wǒ de Xīn” → “월량대표아적심” (or rarely, the transliteration “위에량 따이삐아오 워 디 씬”)
An additional note on personal names
You asked about personal names. Non-Korean names often sound pretty weird, old-fashioned, or funny when read with Korean Hanja sounds, especially Japanese personal names.
There’s a kind of meme where you call Japanese characters with Korean Hanja sounds to give them funny nicknames; one of the cases would be calling the anime character 食蜂 操祈Shokuhō Misaki “식봉食蜂이.”
Yes, since the 1990s, I think, the National Language Institute (국립국어원) made it a standard to Koreanize foreign names following their original pronunciation. So all official speeches and writings (and nowadays in most informal conversations too) now use names like 도쿄, 상하이, 베이징 even though they used to be referred to as 동경, 상해, and 북경.
This seems to be the only reasonable way. Given how the world has gotten smaller, whatever language materials you create might be read by foreigners whether you intended it or not, and they won't understand words written according to Korean hanja pronunciation. The reverse is seldom true because Koreans learn the original foreign names in school, when they travel or get exposed to foreign media, etc.