"Ninafikiri inawezekana kwenda"
Translation:I think it is possible to go
For the long story, you could follow this link: http://www.let.uu.nl/users/Alexis.Dimitriadis/personal/papers/stative-paris02.pdf
But this is highly technical, and to make it shorter, and hopefully easier, some verbs require that you construct the stative form by combining the stative suffix '-eka-' or '-ika-' with the reciprocal '-na-'. For the verb 'kuweza' you would have to add '-ekana' instead of simply '-eka'. Other verbs do this optionally, and the choice can actually sometimes change the meaning according to which form you choose. There are no very predictable rules as to why this happens, so you would just have to remember them by heart.
The most common verbs that require '-ekana'/'-ikana' are:
kuweza -> kuwezekana (is possible)
kupata -> kupatikana (exists/is to be found)
kuona -> kuonekana (is visible)
Unfortunately, the link you provided is not valid anymore: it just redirects you to the Utrecht University's home page. However, the paper is available for download on ResearchGate https://www.researchgate.net/profile/Amanda_Seidl/publication/46648240_Statives_and_Reciprocal_Morphology_in_Swahili/links/5630eb3d08ae13bc6c35490f/Statives-and-Reciprocal-Morphology-in-Swahili.pdf.
PS: It may be that one has to register on ResearchGate to download it
You would use the subjunctive if you needed to add the subject to kwenda
Ninafikiri (kwamba) inawezekana kwenda. = I think (that) it's possible to go.
Ninafikiri (kwamba) inawezekana uende. = I think (that) it's possible for you to go.
Kwamba is optional in sentences like this Swahili, just like it is in English.
If you were expecting the subjunctive on inawezekana, the reason it's not subjunctive is just because that's not one of the uses of subjunctive in Swahili. In formal German, for example, the subjunctive is used for quoting someone else (even your own thoughts), but it's not used for this at all in Swahili. The romance languages also use their subjunctive forms for various things, but in Swahili, it's never used merely to indicate reported speech (or thought).
Reported speech: English uses tense backshift where appropriate, formal German uses subjunctive, Swahili uses indicative:
He said he was sick.
= Er sagte, er sei krank.
= Alisema (kwamba) yeye ni mgonjwa
Expressing hopes and wishes: English uses indicative or object + infinitive, German uses indicative, Swahili uses subjunctive:
I hope (that) he doesn't come.
= Ich hoffe, dass er nicht kommt.
= *Ninatumaini (kwamba) asije.
I want him to go.
= Ich will, dass er geht.
= Ninataka aende.