They'd more likely intervene on Japan's behalf, Russia being Germany's No. 1 geopolitical rival around this time.
Disagree that they would take Japan's side in the 1904-1905 timeframe, see Kaiser's pro-Russian stance and initiative for an alliance with Russia (Bjorko). You would need to go back several years for a PoD to make Germany more pro-Japanese.
From a practical point of view- since the Anglo-Japanese treaty would require British intervention, could such a move by the Kaiser trigger a world war?
Yes, that's why it would be incredibly risky. The Germans would have to assume that Qingdao and the Micronesian islands will be subject to immediate retaliatory attack by Japan (although if joining the war is secretive and well-timed, the Russian Baltic fleet could coal up at Qingdao before the tsushima battle, and unite with the German Far Eastern squadron).
Furthermore, with Japan facing two enemies now, Russia and Germany, Britain is obligated to aid Japan by the letter of the Anglo-Japanese treaty.
So, the Germans also have to assume that the British could go to war with them, and subject German colonies, shipping and fleets worldwide and in German waters to devastating attack and conquest by British and Dominion forces. That is why I think Tirpitz would be dead-set against doing such a move so early in his fleet build-up. He'd tell the Kaiser, "that's the best move for 1920, not 1905".
What would the French response be if Russia is attacked by Britain?
France is in quite a pickle. If Britain attacks Russia, France is going to either lose their only ally by not honoring their treaty, or gain a new powerful enemy by declaring war on Britain. They will be putting their colonies and fleet at great risk in doing so. They will be really unhappy with their options, and trying desperate diplomatic maneuvers (like the Entente Cordiale) to avoid having to make that choice.
By the same token, Britain won't relish the prospect of a war with Russia, Germany and France, that will be an expensive, wide-ranging and dangerous challenge, putting assets in the Mediterranean, India, Persia and Africa at risk.
Perhaps to avoid backing France into such a corner, Britain might try to interpret it's treaty so it only declares war on Russia's second, Germany, and not Russia itself. This could be done in the hopes of satisfying the formal obligation to Japan without triggering a French casus belli. In this way you end up with Japan facing Russia mostly (but with some local German forces in the Far East), Russia facing Japan entirely, and Britain remaining formally at peace with Russia while having its own parallel duel with Germany, and France able to stay a pro-Russian neutral.
If France actively came in on the Russo-German side, it is going to expect the entire shore of northern Africa from Morrocco to Suez as compensation for it's trouble.
Britain would see a danger in the potential of an all-continental coalition, but also a temptation. German intervention in the Russo-Japanese war creates the perfect pretext to "Copenhagen" the German fleet in the north sea and German sea power worldwide. The British could envision an optimistic scenario where a relatively cheap and decisive war sinks both the Russian and German fleets. British taxpayers could save gobs of money on naval construction or maintenance over the next decade. Your thoughts? I think it would be a delicate high-wire act, but just might work, as long as the British and Russians are willing to accept the tactical risk of not just shooting each other on sight.
What's Italy position here as well?
I believe Italy's attitude at the time was more pro-Japanese. Not sure why, but Italy at this time and since Abyssinia seemed to be anti-Russian until Roccogigni in 1909. When they liked Russia it was only for one thing, to screw over Austria-Hungary. That is not at play here.
Italy is capable of remaining neutral here, it long had made clear to its Triple Alliance partners that it would not join a fight against Britain. At the same time, the Italians are not going to actively incur the wrath of Austria-Hungary and Germany by declaring adherence to the Anglo-Japanese coalition, especially with Russia weakened in Europe and France neutral.
At their boldest, the Italians might decide it is time for a private war with the Ottomans over Tripoli.
For the Kaiser this isn't a bad move- he has to fight Britain eventually, so why not get some help and let the French and Russians batter up Britain for him?
It depends on German assumptions.
In the near-term, losses of colonies and overseas trade are inevitable. The German overseas empire is doomed in the face of British Imperial and Japanese seapower (possibly with American intervention in the Pacific thrown in- maybe some occupation of German Micronesia). So is loss of the battlefleet, at least if it comes out to engage and possibly even if it does not.
The medium to long term strategic gains are more speculative and chancy, but the potential is there.
The British blockade of Germany is offset by trade with Russia and France. Between that trade and the lack of a need to mobilize army forces, Germany will continue to be well-fed. A de facto "continental system" is in place, and Germany is its economic leader. Meanwhile, Germany becomes Russia's only source of industrial goods formerly imported from Britain and America. If France ends up in the anti-British coalition, then Germany gets to take over British market share in France.
So, it's a trade-off. Germany, by committing to war on Russia's side, faces a near certainty of losing all colonial real estate and oceanic trade, a risk of losing its entire naval order of battle, but it gains weakening and distraction of its most dangerous potential rivals, Russia, France and Britain.......priceless.
In OTL, Germany thought it could do alright with a free hand but not actually going over the brink into war. Germany at this time did not think war with any power was inevitable. Only if Germany assumed that war was inevitable and its best course would be to ensure it started under the best possible circumstances, would it make sense for Germany to get involved directly as a belligerent.
It would be an incredibly confusing system of alliances at play. What could Germany realistically do to fight Japan though? I guess they could supply and provide aid to Russia, did they have any real force projection in the Pacific though?
Yes it would- as illustrated in the discussion above.
Germany can engage its Far Eastern squadron against Japan, and has bases in Qingdao and Micronesia. In OTL its ships and colonial ports provided coaling services for the Russians, unless the German fleets are interdicted, the Germans can send more fleet units to the Pacific to work with the Russians.
They certainly can supply aid to Russia, maybe some advanced artillery pieces and crews.
They do have force projection capability in the Pacific, but it is very vulnerable to Japanese, British and Dominion interdiction.