SRS is meant to be used every day. When you take weekends off, you get a backlog of due cards.

Actually, I think what SRS does (at least Anki) in such cases is quite smart, if not quite optimal. Yes, it nudges you to clear the backlog ASAP, lest you forget those marginal items entirely. But then if you do recall an item despite the delay, it gives you improved credit for that memory, so you'll be seeing it less frequently. So, all things considered, you can ignore the nudge after some point, with very limited side effects.

Also, the reason you get a backlog in the first place (with no introduction of new items) is that Anki implicitly seeks to implement something close to a mastery-learning strategy. You don't "learn" something only to put it away after some test and let things fade away from your memory - you're supposed to remember everything you've ever put in the deck. I'm not sure how appropriate this is in a language-learning context, since after all there's no such thing as a "complete" vocabulary. But it's definitely good for more formal, rigorous subjects, where forgetting something can spell disaster.