Als "when" / "if"
In English, the difference between "when" and "if" is important. A Dutch person's reversal of the usage can be disconcerting to the native-English listener. We will probably understand by context, but may experience a moment of confusion. Don't say "when your house is on fire" unless that's a normal occurrence or you know it's going to happen.
Anders "or else," "otherwise"
Often translated as simply "else." It works, but is technically incomplete.
Bedoeling "intention" / "meaning"
When a plan goes wrong, the Dutch often say "that was not the meaning." What they are trying to say is "that was not the intention." You can "mean" something in one translation of bedoel. For example, "hoe bedoel je" translates as "what do you mean?" A bedoeling, though deliberate hope of a particular result is an "intention."
Kijken "watch" / "look"
You can only "watch" something if it's moving or changing. If it's not, you look at it. You watch a film, but you look at a painting.
Concurrent "[the] competition"
The English word concurrent is an adjective derived from the Latin concurrere, "to run together," and means "happening at the same time."
Gefeliciteerd met "Congratulations with"
In English, you can't congratulate somebody in honor of the birthday celebrant. You can't really wish somebody a "happy birthday with" somebody else, either, nor is there any other such expression, for use with a fellow guest at an English-language verjaardagsfeest.
Leren "learn, study" / "teach"
You can't "learn" something to somebody; you must "teach" them. When you gain knowledge, you "learn." And, when you actively work to learn about a subject, you "study."
Lijken "looks like" / "is like," or "resembles"
In English, we say "looks like," "sounds like," "is like," etc., to convey similarity. In Nederlands, the verb "lijken" is more inclusive. "Het lijkt op" means that "it [looks, sounds, is, etc.] like." Often the native Dutch-speaking person will mistakenly use the most-common form, "looks like," when that's not always the way we'd say it in English. You can use "looks like" to mean "seems like," in a non-visual sense but not to mean "is like." For example, "it looks like Suzie missed the bus again" doesn't mean you're watching her miss the bus. On the other hand, "Suzie looks like you" doesn't mean that she's dumb like you, missing the bus it means that she resembles you physically.
Recept "recipe" / "prescription"
A doctor can not give a "recipe" for medicine, and you do not need a prescription to bake a cake.
Toch "isn't it?" (for example)
Toch serves as an all-purpose affirmation request that does not exist in the English language. To request this affirmation in English, we follow the relevant statement with a question. This question is formed as a negative of the statement.
"It [does something,] doesn't it?"
"It can [do something,] can't it?"
"He was, wasn't he?"
Commonly used to mean "more than that... (I don't know, etc.)" It works, but sounds cute and Dutch.
Wortels "roots" or "carrots"
You can't refer to a wanderer as somebody who has "no carrots."