……你得到一个州，每个人都得到一个州！

As Switzerland, have 24 states.

「Strategy」

Although the achievement description says you need 24 states, you can get the achievement with more than 24 states.

Historical

On historical, rush the fascist path and join the Axis. As soon as possible, justify on  维希法国. Convert the militia to regular divisions via the focus and create a decent template of infantry and artillery - this will be enough to easily overcome the Vichy army as many units will also be on the border with  德国. Remember that to capitulate Vichy, you also have to take the part of victory points that  维希法国 has in North Africa. An easy way is to build transport planes and research/train some paratroopers. You can paradrop from allied countries which aren't in the war, so simply put your (transport) planes in the airfield on Sicily. The fighter / CAS planes you get at the start of the game should be enough to get air superiority. From Sicily, you can reach Tunisia and a small part of Algeria. Alternatively, you could do a collaboration government on  维希法国. Due to  维希法国's large colonial holdings, you will have over 24 states after annexing them in the peace deal.

When you join the Axis, do NOT accept their requests to join their wars or their requests to help you with yours. If you do, Vichy France will join the Allies and you won't get your states until the final peace conference at the end of WWII (if at all). In fact, as soon as Vichy France is capitulated, you may want to leave the Axis. This way, you can keep cordial relations with both Germany and the UK for a few years, and, when the war goes badly for Germany around 1944, you can declare on them (and maybe even get an invite into the Allies), landing 我不是被关在这里陪你…….

Non-historical

The following strategy works best if Germany does 反对希特勒 and Italy stays Fascist, but it can be done if those aren't the case.

On non-historical, rush down to Press for Vorarlburg和Preempt Anschluss. You'll need to make sure that you are moving the balance of power scale so that it is on the Council side. As you get close to the two aforementioned focuses, improve relations with  奥地利 (the AI rarely refuses to give up Vorarlburg or all of Austria if Austria has 50+ favorability with Switzerland). If  奥地利 is annexed by a different country ( 德国,  匈牙利, etc.) before you can do Preempt Anschluss, if Hungary annexes Burgenland, or if Austria refuses to hand over their land, restart the game (unless you really want to go to war). Once you have all of Austria, work to lower your Democracy support below 60% and increase the balance of power to "Full Council Control". Make sure that you're saving at least 150 political power each December to elect a new council member.

Once your Democracy support is <59.9% and you're at "Full Council Control", do the focuses "Demand Italian Alps" and "Demand French Alps" (make sure you have good relations with each of those nations too). It doesn't matter which one you ask first; use your judgement of how the game is going and who's fighting whom to decide. Be aware that if either country is at war and has lost control over any of the needed states, you won't get them in the deal, so if it looks like France or Italy are about to be dragged into a defensive war, ask them first. Once the AI gives you the French provinces east of the Rhone (Var, Savoy, Bouches du Rhone, and Alpes) and the Italian provinces north of the Po (Piemonte, Lombardia, Trentino, and Alto Adige), you'll have 19 total provinces, which you can core by either taking the "The Alpine Protectorate" focus or by spending 100 political power to declare the  阿尔卑斯联邦 from the events tab. Once you've cored the Alps, simply find a country that has land you want. You can either continue to lose support for Democracy and flip to another ideology that allows you to justify and declare wars; you can take one of the focuses that let you declare war on  法国,  德国, or  意大利; or you can join a faction that's at war. An easy way to get deliberately drawn into a war is to guarantee independence on  希腊 (as long as Fascist Italy is still in the game), since Fascist Italy will declare war on it soon enough. Build up your army - you'll easily churn out divisions once you core the Alps, and use the "Alpine Redoubt" focus to build land forts on every single province you own. Since you already have most of Northern Italy, your march down the peninsula will be rather easy. Once all of the majors in the faction you're fighting surrender, simply annex the 5 needed states and the achievement will fire after the peace conference ends. If you want to get the 瑞士奶酪（Swiss Cheese） achievement, annex 5 non-contiguous states in the conference.

If you want to continue playing after you've earned the achievement, save up about 750 political power and oust the confederation president (and elect new members so you don't get hit with the penalty) - that should move the balance of power scale back to a spot where you can begin running the "compromise with cantons" decision. Run that as needed until you get the balance of power to where you want it to be so that you can do the military focuses that you weren't able to do while rushing the land-grab focuses.