Can 2 light bulbs of 120V in series be used on 230V AC?

It is possible, as long as they use the same power (or resistance).

However, it comes at a risk. If one of the bulbs uses less power (for whatever reason, maybe damaged/end of light ... see Ferrybig's remark below for a good reason), the other uses more, and will break (faster), so it's not a perfect solution.

Because of P = V * I <=> 150 = 110 * I, I = 1.36 A for two bulbs, which is 0.68 A per bulb.

For the 220V way: P = V * I <=> 150 = 220 * I, I = 0.68 A per bulb.

I feel that it is not a good idea as a standard practice. But conceptually, it would be fine to use two 120V filament type light bulbs in series on a 230V system. I have done it before, briefly, and the bulbs appeared pretty normal. So feel free to experiment. But in the long run, maybe the bulbs would not share voltage equally and one will fail prematurely. Not sure.

Yes, the brightness would be close to 2 230V bulbs in parallel.

Yes, it would work with a dimmer.

NOTE: This answer applies to filament-type bulbs (incandescent bulbs). It would not be a good idea to put LED bulbs or fluorescent bulbs in series because their internal electronics are not designed for that.

NOTE 2: I am not sure this is a big deal. Usually on a light bulb, the center conductor is "hot" and the outer, more touch-able conductor is "neutral". In series in a 230V system, one of the bulbs will have the center hot, and the outside at high voltage (half of "hot," or 115V). You could argue this is the tinyest bit more dangerous than standard 120V systems and bulbs. But as long as you don't touch either conductor it should be OK.

In theory, if it's really no electronics bulbs, you can do this. The lifetime of the bulbs may be lower as they need not divide the power equally as they age, and larger power means larger wear.

In practise, yes, it will work and will do what you expect. Unless something goes wrong.

Still, it's very likely against the electricity code in any European country, as your bulb is a device rated probably for 100--120 V, so it can never be connected to 220/230V mains. And there are good reasons for this as there are safety issues: Imagine you (or anyone else that happens to be staying in your house, even just for a visit) replaces the bulb with a 220V one, or even a 120V one with different wattage. Then you will expose one of bulbs to >120V, and they were not rated for this. Second, you should not wire this yourself and a certified electrician should never be willing to do anything like this. Also note that if you had an accident, the insurance company would likely claim you responsible as in their point of view, you would have been simply messing up.

You are solving the wrong problem. Just invest into some high quality LED bulbs, they need not be expensive. You can get 600-lumen CRI 80 LED bulbs for as low as EUR 2. Is it really worth messing up with the electricity?

Yes, it's not Code legal (because the shell of the upper bulb socket will be hot), but it will work. This depends on the bulbs being equal; if they're not, one will burn out first.

However, given the Code violation and the general difficulty, I think you're barking up the wrong tree. Fluorescent technology has gotten absolutely fantastic in its sunset years, and there's no problem getting full-spectrum fluorescent tubes at any color temperature you desire. The light is higher quality than is possible with LED (really).

The tube doesn't need to be compatible with one mains voltage or the other; that's the ballast's job. And two things are true about ballasts. First, you can get native European ballasts for standard fluorescent sizes. Second, modern North American ballasts are multi-voltage compatible from 110-277 volts, and 230V is in their midrange.

It's also vastly more efficient, with lumen efficiency near LED, so the additional up-front cost will be paid by your reduced electric bill.

You can also explore LED options, but there's an ocean of fair-medium quality out there, and top quality LED is still pretty hard-to-find and boutique priced.