Is there any difference between 'strongly recommended' and 'highly recommended'? Or both one is totally same?
Strongly recommended means the recommendation comes to you 'strongly' ie you are being powerfully urged to do, or not do... something.
Eg it is strongly recommended that you don't stick your head out of the train window when passing through a tunnel. (ie - don't do it)
Highly recommended means more that the person has a high opinion (ie a good opinion) of the thing. They are saying it's great, but there is less sense that they are urging you to try it.
Eg This person comes highly recommended for the role of tuna canner (so, they have a high reputation). But there's less exhortation to hire them, it's more for your information, than telling you what to do.
There is certainly a degree of overlap when these are used in this way:
This new book on grammar is highly / strongly recommended.
However, this disguises the fact that 'strongly' is more of a verb-modifier, and 'highly' somewhat more of an adjective-intensifier.
You are strongly recommended to have your car serviced yearly.
Ann's entry was highly recommended.
show non-interchangeable usages.
It's actually wrong to say "I highly recommend this," and I'll explain why. You should say "I strongly recommend this." The reason is that when you say that something is highly recommended, you mean that it is recommended by those with great credentials for recommending it. For example, if I say that a particular wine is highly recommended, it means that it is recommended by wine experts with decades of experience. They are highly qualified to make this recommendation.
If you say that you highly recommend something, it's a bit weird. For one thing, it doesn't really work in the active. It better lends itself to being used in the passive. Also, you are kind of boasting about your credentials, saying that you are highly qualified to make this recommendation. It's better to say "I strongly recommend this."