al panav and al hapanim

Here are two Hebrew expressions that sound very similar, but have very different meanings.

"Al Panav" על פניו  - literally means "on it's face", and can be translated as "apparently".

"Al Hapanim" על הפנים -  literally means "on the face" and is a slang term meaning "the [situation/thing] is terrible."

The origin of al panav is easier to determine. It comes from the English "on the face of it", which likely originates in the Latin prima facie (at first face). It's not an ideal Hebrew phrase, as there is an existing word in Hebrew with the same meaning - לכאורה lichora. However, as this site points out, if you really want a similar sounding phrase, then al pnei hadevarim על פני הדברים is closer to being correct.

Al hapanim is a harder one to crack. According to the same article I quoted above, it doesn't appear in the older slang dictionaries. All I've seen so far are speculations, but they all seem reasonable.

In Rosenthal's Dictionary of Hebrew Slang, he suggests it comes from the English "to fall flat on your face" (an expression which fully translated into Hebrew made it into Yehudit Ravitz's 2000 song געגוע - which contains the lyrics איך לא ידעתי לא ליפול על הפנים).

Nissan Netzer in his Hebrew in Jeans - the Image of Hebrew Slang, says the origin might be from Yiddish, which also have expressions meaning "to fall on the face".

This article (not sure who the author is) has a few more suggestions. They quote another Yiddish phrase meaning "his face fell", which is similar to the biblical נפלו פניו naflu panav (see Bereshit 4:6). They also mention that Yiddish, Russian and English all have phrases meaning "a slap in the face" - so perhaps one of them influenced the Hebrew.