I've been impressed with the Skinomi Techskin that I've put on several cell phones. It doesn't care if you leave bubbles as they seem to go away. I even had a piece of large dust get on one phone and though it looked terrible immediately after the install, a few days later the air gap around it was gone and the spec of dust very unnoticeable.
Skinomi TechSkin - Cell Phone Cases, Screen Protectors, Skins, Shields, Covers
Cell phones in other countries really depend on your particular carrier and what you really plan on doing more of as well as the particular country you are in. Though I'd think Europe more standardized than some other places. However I haven't been back to Europe since cell phones were even a thing.
Text, Talk or browse, be aware of what the plan limits are on each. Even with a unlocked phone, your own carrier might have a inexpensive plan you can do for a month. Particularly if just data and text is all you need. In some cases it might be cheaper to buy a burner phone for over there and forward your number to it. And there are week long or month long plans you can buy and just swap a sim card, but be sure to look for the gotcha's.
Friends that have recently done the trip can be a help here. Find out if they had horror stories or it was a non issue for them.
And so this isn't just random foo conversation in the wrong forum. Lets make it bicycle related and say that the color of your bike and the type of cyclometer you have might be faster in one county than in another. But only when lighted with the proper light and video'd by a sports action camera made for cycling.