Flashing English ROM on Korean Samsung Galaxy S3 I got my Samsung Galaxy S3 (SHW-M440S) but it was bought from South Korea. At first, it was all Korean. But after some time (or some tweaks), I managed to set it to English. (No, I am not a Korean).

Can I flash the firmware to a real English version (using ODIN or any other software)? I entered the model number because I might do something wrong but everything is in Korea (SHW-M440S firmwares).

Another problem on my phone is, it will only send an SMS if it has 80 or less characters on the message.
I wouldn't advice this, you can see other questions on here about people asking if they can use different model numbers on their phone and everyone says no. 

A suggestion to you would be the following, go on the XDA website here link and type in your phone AND model number into their search bar. From there you should be able to click on their forum for Android Development, from there you can select a Custom Rom to flash to your phone

As you said you are new it is required to firstly root your phone before flashing a new ROM, as you haven't provided your Phone Model I cannot give you a direct link on how to root your phone, if you can update this detail I could find you a link afterwards. 

Also if you decide to root your phone flash a custom rom please note that it is your risk, doing so will void your warranty and if you end up with a bricked device(not working) I or anyone giving instructions in any links you use cannot be help responsible.

With regards to the problem with only Sending a SMS if it's 80 Char or less, I am not 100% sure as I haven't experimented with various different Custom ROMS but there may be a option that you can select to try and fix it, personally I would post another Question on this website just for that issue

All the best