Open-Source Online Testing Platform

I want to build a self-hosted online testing platform for language proficiency and competitive exams.
The entire system must use only open-source, forever-free libraries and frameworks.
No paid APIs, no usage-based services, no SaaS dependencies.
The platform will be hosted on my Linux VPS (Hetzner) and should be scalable.
Core Functional Requirements
1. Speech Processing (Self-Hosted)
Record user speech via browser
Store audio securely
Convert speech to text (STT)
Analyze:
Pronunciation accuracy
Fluency
Grammar & spelling
Content relevance
Generate automated scores
2. Read Aloud Test
Show a paragraph on screen
User reads aloud
Match spoken words with displayed text
Score based on accuracy, pronunciation & fluency
3. Repeat Sentence / Audio Speaking Test
System plays an audio clip
User repeats it
Compare spoken response with original reference
Auto-score similarity
4. Supported Languages
English
French
Spanish
German
5. Question Types
MCQs (text / image / audio / video)
Fill in the blanks
Dropdown questions
Reorder sentences/paragraphs
Essay / writing tasks with AI-based evaluation
6. Exam Features
Timers (section-wise & question-wise)
Word counter
Highlight grammar & spelling mistakes
Auto-save responses
7. Admin Panel
Create/edit exams
Add/edit questions
Upload audio, image & video
Configure scoring weightage
8. Compliance & Constraints
Open-source libraries only
Fully self-hosted
No paid APIs (Google, OpenAI, Azure etc NOT allowed)
Clean, documented, modular code
Docker-based deployment preferred
Preferred Developer Skills
Python (FastAPI / Django)
Speech Recognition & NLP
AI model integration
Online exam platforms
Open-source deployment