I suspect that those who have trouble with multiple languages only speak one. This may be an unfortunate side-effect of having English as your native tongue, since it is so widely spoken. But more people probably speak multiple languages than only one, and those who do have no problem at all mixing and switching between them. Fear of 'foreign' language influence is just fear of the unknown. Children who grow up multilingual do not suffer any confusion and have no trouble keeping their languages separate when they need to. 

Language is a wonderful and amazing thing. We think in words. New words expand our thought process. Having borrowed words at your disposal can add precision to definitions for which native words are insufficient. A hackneyed example of this is the Inuit word for snow, which is actually around 50 or so words. These exist because a detailed understanding of the different states of snow is important for survival in places where snow is a common feature. No doubt English has more words for money.

People need to quit fearing our indigenous languages and start embracing them for all the richness and distinction they can bring us. Tourists like cultural differences that make a place unique. That is why they travel. If every place was the same they would just stay home. 

One of the great benefits of the British empire (which does not, of course, make up for all the drawbacks), is the rich variety of English versions that have evolved throughout the former colonies, drawing on local language influences. Indian English is not the same as Australian English, which is different from Fiji and America and Kenya and New Zealand and all the rest. This is very much to the benefit of all speakers, who are able to communicate with each other in spite of the differences. The more English vocabulary expands, the better it becomes. This is something to be celebrated.