You really need to get a job. And if you already have one, take a second job. Or even a third one! Cause you really seem bored out of your mind, if not downright racist.
Is this your problem in life? A foreign neighbour hanging stuff on the fence? The fence is common between the 2 properties.
Also, you noticed your neighbour doesn't speak English, and you still think at doing passive aggressive stuff. Take a picture of your side of the fence, draw a big, diagonal, red line over it, add a smiley emoji underneath for politeness and hang it so they can see it on their side.
Or, buy them an additional drying rack, to improve the relationship between you and them. 100% they'll take it out and use it, as a polite gesture towards you.
Or even better, don't do anything. They'll soon realise in UK it rains so much, it's not really worth hanging stuff out.
Always remember that when you sell the property, you have to disclose any conflict you have with the neighbours. And existing conflicts can lower the value of the property. So think 1000 times before being petty with your neighbours, foreigners or not.