I've always understood Weltanschauung as being 'a comprehensive worldview'. Worldview by itself, on the other hand, I've taken as a category that is modifiable not only in the sense of 'comprehensive worldview', but as in 'limited worldview'.

I have the sense that Weltanschauung implies an understanding of the world, systems of humankind, or Cosmos, that is deliberately or logically understood and fully-formed, such as that underpinning an extensive philosophical system.

In practice, the shades of difference in the two terms will be dependent on the speaker or writer, with the terms becoming synonymous in cases where worldview is intended to capture the comprehensive sense of the German antecedent.

Usage of weltanschauung in English

The OED has example citations from 1868.

A blog post here on "Weltanschauung in English says gives an interesting referenence:

Google's new, fascinating Ngram tool shows you that it all started in 1850.

Both the post and link open the Google Ngram viewer.

Examples

Weltanschauung [from the OED]

1868 W. James Let. in R. B. Perry Thought & Char. W. James (1935) I. viii. 160, I remember your saying‥that the characteristic of the Greek ‘Weltanschauung’ was its optimism. 1906 Nature 10 May 26/2 In 1863 Haeckel entered the lists as the champion of the evolutionist ‘Weltanschauung’. 1917 A. S. Pringle-Pattison Idea of God iv. 69 The intimate appreciation of living experience forms the basis of the whole Weltanschauung which he [sc. Bergson] offers us. 1934 M. Bodkin Archetypal Patterns in Poetry 326 A man's philosophy‥ is his Weltanschauung—the individual vision, or perspective of reality. 1952 G. Sarton Hist. Sci. I. iv. 121 The creation of that astrological Weltanschauung which dominated late ancient and medieval thought and is not yet extinct today proves the survival through the Dark Interlude of some astronomical ideas of immemorial antiquity.

weltanschauungen (plural)

[from the OED]

1978 N. Jardine in C. Hookway & P. Pettit Action & Interpretation 124 Speakers of different cultures, having different Weltanschauungen, ideologies, interests, paradigms, etc.

worldview

Er, just substitute "worldview" for "Weltanschauung" in the sentences above.

More examples:

But I will say that their worldview is aggressively offensive and that a game that I might've tried is now something I won't consider because of their steadfast, intolerant stance. Michael Grove