(From Reddit of Violet Evergarden)
I'm Japanese so it seems I must answer your question. As for me, I say "Aishiteru" to my wife about once a month especially when she is exhausted. When right after I married her, I said about once two days... This is so embarrassing! Also, I say "Aishiteru" to my children once a month. I think this frequency is even higher in Japanese.
Basically "Aishiteru" and "I love you" are so different. The former is very dramatic, like confessing your romantic feeling and the latter is ordinary for family. We usually say "Are you fine?" or don't say anything but just smile gently or show empathy for them.
I think the alternatives to the "I love you" for Japanese are simply "I'm going", "take care", "I'm home", "welcome back", "hello", "Good morning", "Good afternoon"... greetings. Us Japanese think greetings are quite important (I think you too). Probably almost all families discipline kids for many and many times not to forget greetings. I think they are replacement for the "I love you".
In my opinion, the Japanese don't like straight expressions, while it:s recommended to speak your opinion and debate in some western countries. Us Japanese like ambiguous opinion and pick up them so that it looks as if there were no conflict. Maybe it's because we live on islands, we are an (almost) single tribe, our culture has small diversity, we don't have the religious discipline... we have had fewer times to debate in everyday life.