Tips for fluent speaking without engaging with native speakers?

[rdearman]

I think you need to talk, simply because you need to make the "muscle memory" in your mouth and throat and tongue such that when you speak it all happens in the correct way. So in theory, you never need to engage with a native speaker., self-talk and shadowing should be sufficient.

However.... Is your pronunciation correct? Is your accent so thick a native can't actually understand anything you say? The only way to test this is to actually speak to a native. Someone willing to critic and criticize your language skills and give you pointers. I've met quite a few people who think that they are speaking perfect English, but I couldn't understand what they were saying because the accent was so thick I couldn't figure it out.

You mean Scots?

LOL. Only Glasgow. No, the people I was thinking about were Russian.

[Iversen]

(...) I couldn't understand what they were saying because the accent was so thick I couldn't figure it out.

You mean Scots?

This is not limited to Southern Brits lamenting about Northerly dialects or of Scots. I recently watched a French TV program where someone found it necessary to put subtitles on because a person spoke Québecquois, and in another program they put High German subtitles on because the language spoken was a mild version of Swiss German. And in Denmark jerks in Copenhagen have even put subtitles on nationwide TV when somebody spoke a Jutish patois.In none of these case did the speakers use the more extreme versions of their dialects, so the blame for being too lazy to even trying to understand their fellowmen (and -vomen) must lie squarely with the native speakers of the dominating language forms.

And if those native speakers can't even understand other native speakers with slightly different vernaculars then it is understandable that they also have problems understanding language learners. Luckily there are also people who actually do an effort to understand other human beings. And I mostly wait so long having conversations in my target languages that I rarely meet a totally blank face - and if it should happen I would not necessarily assume that it was my fault.

And of course there are language learners with such a lousy pronunciation that it is comprehensible that nobody can understand them. The blame goes both ways...

[leosmith]

it's possible to fluently speak in a foreign language by oneself by using techniques such as shadowing, self-talk (either aloud or inner coversations/thought process) and extensive reading and listening

I don't agree with this; it's much better to use real native speakers. Unfortunately, German language partners were hard to find for me, so I paid the very high prices tutors ask for on Italki. So I understand why you might want to try this and just wanted to mention that you can also use free AI voice to voice options for pretty realistic conversations. You can set up the ground rules for role playing ahead of time if you want to, and make it even more realistic.