Roughly? Yes.
But the cultural nuances are still different.

The most likely equivalent of Finnish sisu would be the Japanese cultural concept of 我慢/gaman.

Both words:

• are important, typical and admired concepts in their own culture, and manifest in a variety of ways and situations.
• describe a kind of stoicism in the face of adversity. The act of bearing something without showing outward signs of suffering.

The two are not quite the same, though.

From what I read over the years sisu, on its own, also includes a level of boldness or fortitude. Meaning you not only “bear” what’s coming. You also react to and engage it, you actively attempt to overcome it. It may even imply an undercurrent of quiet heroism.

我慢/gaman, when considered on its own, is different from that. It describes an admirable but strictly passive kind of enduring, a stoic acceptance of the bad things that come at you. It may hurt, but the whole point is that you swallow it all without reacting to it, without changing from it.

Mind you, Japanese has words and ideals for “powering through adversity” or “courage in the face of disaster.” A common modern language example for this would be 根性/konjou meaning guts, grit, determination or “balls.”

Why did I not pick that one, then?

Because, although it represents the fortitude angle of sisu well, it lacks the nuance of stoicism. And also because traditionally, the word konjou is nowhere near as central to the Japanese cultural self-image as gaman.

So yes, Japanese has a word “like” sisu: gaman. But the underlying cultural concept still has different nuances and emphasis. If you want to represent sisu as a whole, you will most likely have to use several words in Japanese.