I own 3 personal blogs under one account at blogspot. One is in English & the other 2 in other languages (which are not mentioned under Adsense rules). I want to apply Adsense for my English blog & if I get the code, can I put this same on my other 2 regional language blogs??
Yeah. One account is sufficient for many sites (if you own them!) and no need to open duplicate account which is prohibited under TOS.
You can add Adsense to the other blogs and you don't need to ask Google for approval. Just check if they are OK with the Adsense TOS.
Hyderabadi can you tell me what languages you are using on other two blogs . If they are Indian languages than its ok .
Another question is: Other than these 3 blogs, I have one more but with a different google account (i.e. registered with a different email ID) Can I also put the same adsense code on this 4th blog??
Yes, you can add your adsense in multi blogs. Besides, other languages (Non-english) is allowed by adsense also.
That's not an issue here. You can have one accounts for multiple sites/blogs but your main concern is whether the sites/blogs which you place your codes on do contravene any of the google's TOS