bedauerlich
regrettable
Expresses that something is a pity, unpleasant, or to be regretted.
Es ist bedauerlich, dass du nicht zur Feier kommen kannst.
It is regrettable that you can't come to the celebration.

regrettable
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regrettable
Expresses that something is a pity, unpleasant, or to be regretted.
Es ist bedauerlich, dass du nicht zur Feier kommen kannst.
It is regrettable that you can't come to the celebration.

The adjective 'bedauerlich' (regrettable) belongs to the verb 'bedauern' (to regret). If something is bedauerlich, then it is something that one regrets or finds a pity.
Sein plötzlicher Rücktritt ist sehr bedauerlich.
His sudden resignation is very regrettable.
'Bedauerlich' (regrettable) is very often used in the fixed structure 'Es ist bedauerlich, dass ...' (It is regrettable that ...). This is followed by a subordinate clause that describes what one finds unfortunate.
Es ist bedauerlich, dass das Projekt nicht finanziert wird.
It is regrettable that the project is not being funded.
'Bedauerlich' (regrettable) is a rather formal word. It is often used in written language, in official statements, or in polite, distant conversation.
Wir finden diesen Vorfall äußerst bedauerlich und entschuldigen uns dafür.
We find this incident extremely regrettable and apologize for it.
unfortunately
'leider' and 'bedauerlich' both express that something is a pity or unpleasant. The most important difference is the part of speech and the sentence structure. 'leider' is an adverb and comments on the whole sentence: 'Leider regnet es' (Unfortunately, it is raining). 'bedauerlich' is an adjective and describes a thing or situation: 'Das ist bedauerlich' (That is regrettable). Learners may confuse the words because both show almost the same attitude. A practical tip: if you are introducing a whole sentence with regret, use 'leider'. If you are describing something as unfortunate, 'bedauerlich' fits.

Es ist bedauerlich, dass wir die Reise am Wochenende absagen müssen.
It is regrettable that we have to cancel the trip this weekend.
Bei der Arbeit kann ich leider nicht zum Konzert gehen.
Unfortunately, because of work, I can't go to the concert.