This is purely a commercial decision. You can go along with what they want, and risk having the hassles of dealing with a foreign court if the worst happens. Or, you can insist on stipulating that any dispute will be heard in England, and risk losing their business.
Only you can decide which is the greater risk, and which is the least favourable outcome.
That said, where did this contract come from in the first place? Presumably, you were approached by a potential advertiser, and somewhere along the line, they sent you their standard contract. Is that right? If so, you should never have let that happen. What you should have done is to draw up your own standard contract, and have the customer agree to that, rather than the other way round. The contract doesn't have to be particularly complicated, nor does it have to be drawn up by a lawyer. It just need to cover the essential points, all of which should be pretty obvious. The point is, it is up to you to take the initiative.