This would be a joke if it wasn't so serious..https://youtu.be/5k_szrJPYn8
The allegation from pro-Navalny commenters seems to be that the Russian state is using its legal system, both civil and criminal, to harass Navalny. I assume this is with the aim of neutralising him as an opponent of the Putin government.
As I see it, there are three fundamental questions:
1. Was Navalny tried fairly for the underlying offences?
2. Were the civil cases heard fairly?
3. Is there any evidence of Russian state involvement in the poisoning of Navalny?
I can't comment informatively on 1 and 2 because the facts seem obscure, I don't speak much Russian and I have no knowledge of the laws of Russia. The usual suspects in the West seem to think he has been treated badly, including most of the Western media and the ECHR. Very frankly, I do not trust these sources on this issue. In my view, they have an agenda against Putin, for a mixture of geopolitical and ideological reasons.
Vladimir Putin is a Russian nationalist and Russian Orthodox social traditionalist. The Western hegemony is liberal-internationalist and socially-liberal. Putin favours a more traditionalist and conservative basis for Russian society than would be considered acceptable in the West.
Putin's foreign policy strategy leans more towards non-interventionism. He seeks to expand Russian influence among its immediate neighbours in the clear interests of Russia. The most well-known example of this is the Ukraine. This conflicts with Western strategic objectives, especially those of the United States, NATO and the European Union. The West is aggressively interventionist.
Putin's highest moral is the good of the Russian state, as moderated by God. The West's super-moral orientation is less clear-cut. Is the pursuit of equality and liberal-democracy as goals per se just a means to rationalise Western geo-strategy? Or is the West truly in the thrall of these ideas? Or is it a combination of the two? In a sense, Russia is culturally a Western state because as a country it shares the Western Christian axiology, but what Putin stands for is more than a negation of Western liberalism, it is a radical departure grounded in Russian history: Russia's geographic position, its Slavic ethnic identity, the separation of Western and Eastern churches, the industrialisation and modernisation under Bolshevism, and so on.
This brings me to what I think is the central point: Navalny is a Western-facing Russian and in the pockets of Western liberal-interventionists who want to 'Westernise' Russia. Putin is the ultra-parochial Russian resisting this, instead favouring illiberal non-interventionism (i.e. nationalism). This is why I am willing to defend Putin and don't trust Navalny or his defenders. I don't believe Britain should be getting involved.
In regard to 3 above, it is common ground that Navalny was hospitalised in Russia itself after falling ill on a flight, but from this point the facts become doubtful. It is said that he was poisoned, but some pro-Putin commenters are denying this. The evidence of the state's involvement in poisoning him is thin on the ground. Was Navalny poisoned? Why did he have to seek treatment in Germany?
His sentence was for breaching the conditions of an earlier suspended sentence for embezzlement. His defence must be that having been poisoned, he couldn't comply with the conditions, and I suppose he would defend his decision to leave Russia on the grounds that he believes the Russian state is trying to have him killed.
I am no expert, but given all the facts, an English criminal court could activate a custodial sentence in similar circumstances; it would depend on whether the poisoning had occurred as a result of activity that was in itself in breach of the conditions and also whether, having been poisoned, he was acting on reasonable medical advice in leaving the country to seek specialist treatment.