> Isn't it difficult to adapt to left-side driving while having used to right-side?

You get used to it after a few minutes. It takes a bit more concentration, especially when turning out of one-way streets, but it's otherwise fine.

There are mutual recognition agreements between many pairs of countries. The UK, for example, will allow you to directly exchange a licence from an EU or EEA, a British Crown Dependency, or a 'designated country' (Andorra, Australia, Barbados, British Virgin Islands, Canada, Cayman Islands, Falkland Islands, Faroe Islands, Gibraltar, Hong Kong, Japan, Moldova, Monaco, New Zealand, Republic of Korea, Republic of North Macedonia, Singapore, South Africa, Switzerland, Taiwan, Ukraine, United Arab Emirates and Zimbabwe) for a British licence with no need for a retest. Most of those countries drive on the 'wrong' side of the road.