Can politicians hold political rallies while visiting a foreign country? The simple answer is: Yes. As a matter of fact, if these politicians are not banned from visiting the country for some reason, and if the two countries in question have friendly relations, there shouldn't be a problem. This, of course, is true when talking about democratic countries.
The matter is important because some politicians in Germany and the Netherlands have made it clear that they don't want Turkish officials conducting an election campaign for the upcoming constitutional referendum, with other European countries possibly following in their steps.
Globally, there is no doubt these European countries are perfectly "democratic" and that freedom of expression and of demonstration are "far more respected" there than in Turkey.
Are the civil society organizations who have invited Turkish officials legal? Yes, they are. May those Turkish politicians who want to speak in Germany or in the Netherlands legally enter those countries? Yes, they can. Yet, Turkish government officials are not being authorized to hold rallies. Perhaps Turkey's relations with these countries are not that friendly, after all.
Banning rallies is of course not enough to indicate that relations are indeed declining between Turkey and these countries. Perhaps these countries are opposed to having Turks hold political rallies for other reasons. One could always criticize them because they don't respect the freedom of expression, of course, but let's imagine that they have a legitimate reason to prevent the rallies. Let's say they don't want Turkish politicians to meet with Germany's Turks because such an event could harm those people's integration process into German society. Or let's imagine that German or Dutch authorities have concerns about security or public order.
Still, if these were really the reasons behind not wanting those rallies, concerned authorities from both countries could come together, discuss it and try to find a mutually acceptable solution. Cancelling events at the last minute is certainly not a friendly way to deal with problems.
One may say there is more than enough to indicate that Turkey has strained ties with those countries. There is one more detail, though. Do those countries treat all politicians from Turkey in the same way? We know they don't. Only politicians from the current governing party are being banned, while other politicians from Turkey do what they want.
As a result, local and federal governments in these countries have made their preferences very clear about Turkey's political life. While some Turkish politicians are acceptable, others are not. One wonders if those authorities act the same way with all the countries.
We don't know how they treat every politicians from divergent countries, but it is obvious they have double standards about Turkey. It appears those local and federal authorities have made their choice, and they just don't like Turkey's current governing party. It would be wise for these countries to keep in mind that who is and who will govern Turkey is determined solely by Turkish voters, not by them.
The main problem is that this crisis has the potential to hurt social relationships between the involved countries. It is obvious that those decisions, even though made on the local level, will have an impact over Turkey's diplomatic relations with those countries. Perhaps this is exactly what the local politicians are trying to do: they want to sabotage their governments' policies toward Turkey, consequently influencing their domestic political balances in their own countries.