How much impact does geo-targeting have?

Hello. I am currently running a website in Korean language, with English as the website language, with server located in Japan. (We are working in Japan)

I recently discovered that when searching in Japan, different search ranking comes up as a result. For example, for keyword A it would rank 3rd in Korea but it would rank like 15th in Japan.
Sometimes it works differently and keyword B would rank somewhere below 20th in Korea but rank 1st in Japan. (All keywords are in Korean)
So I dug some more and found out that all my website's hreflang attribute is set in en-US.

Here it comes my question: will my website rank better if I changed my website language to Korean?

Also found out about existence of these two terms below, but I don't know which is more effective. I don't plan on using language other than Korean to serve my website.
og:locale, hreflang ... What is the difference?

Definitely! Korean language will rang better than foreign language for your Korean keyword.

If you want your Korean website to show up better in Japanese searches - change the language setting to Korean and make sure the hreflang attribute is set to " ko." also, focus on using og:locale for accurate regional signals

Thank you guys! I will make necessary changes and see if it works better.

healing really does play a role I think.

but be sure using unique text if you translate English version to Korean. Even if 2 content are different language, if translated . Google thinks it s duplicate

SeoIsArt said:

but be sure using unique text if you translate English version to Korean. Even if 2 content are different language, if translated . Google thinks it s duplicate

Click to expand...

Thank you! I think I am safe in that regards though.
I built my website all in Korean language not using English at all, just my websites settings are in English so that I can work better.
So there is no English contents to begin with.
I now have to work with my wordpress website in Korean, which is kinda problematic because all this time I've been using English... haha

Geo-targeting can have a substantial impact, especially on ccTLDs or when using Google Webmaster’s geo-targeting settings. Since your content is Korean, setting hreflang to ko-KR would tell search engines who your intended audience is, which could improve your SERP positions in Korea. The hreflang tag is essential for language-specific or regional targeting

How much traffic do you get?

As said, it is better to change the language of your website to the KOREAN.