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By Mockly English · Last updated:
How a Belgrade Tech Lead Practised System Design Interviews in English
HR screens were fine. Solving out loud in English was the round that broke.
At a glance
| Role | Senior SWE / architect / tech lead (pivoting toward management) |
|---|---|
| Region | Belgrade, Serbia |
| Starting Point | HR fine; could not solve out loud in English when stressed |
| Target | English-speaking role (London / Spain / Cyprus / Dubai) |
| Outcome | Design + coding mocks alongside live processes (Revolut, Perplexity, etc.) |
Timeline
Senior / tech lead
Focus
Belgrade
Outcome
Design + LeetCode in English
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“I know the solution. When I am stressed I cannot deliver it in English without losing the plot.”
The Problem
He had eight or nine years as a software engineer, a senior/architect/tech-lead seat, and a management book pile. HR interviews were not the problem. Algorithms and system design in English were. Under stress he could not focus on delivering the solution in the language. He wanted everything that changed the result of the interview — not a conversation club. Live processes were already moving: Microsoft, Booking, Databricks had started; Yandex and Nebius were in play; Revolut and Perplexity had rounds on the calendar.
What We Practised
The hour looked like the round that scared him: a problem on the board, English on the delivery, stop when the plot disappeared. Design chapters became spoken drills. Behavioral stayed secondary.
- LeetCode out loud under stress
- System design as a performance (large-system examples)
- Some behavioral for a tech-lead to manager pivot
- English that transfers between companies already in process
Useful references along the way: What to expect in English interviews, STAR interview framework.
Starting Point
Belgrade. English-speaking job as the main goal. Gym, friends, tea. Design practice included large-system chapters (video, drive-like storage) as study material — not as a claim that those companies had already interviewed him. Coaching had to match LeetCode, system design, and some behavioral, while real loops continued.
Before and After
Before coaching
- HR was easy; technical English was not
- Could not focus on the solution while speaking
- Stress destroyed fluency
- Multiple live processes with no stable spoken scaffold
After coaching
- LeetCode with a think-aloud checklist
- System-design performance, not only reading chapters
- Light behavioral for the lead/manager pivot
- Same English habits across Revolut, Perplexity, and the rest
Session snapshot
| Experience | 8–9 years; senior / tech lead |
|---|---|
| Weak round | Algorithms + system design in English |
| Live processes | Revolut, Perplexity, others in notes |
The Result
Notes do not record a Google interview or an offer. They record a Belgrade tech lead who could pass HR and still fail the spoken technical round, while several companies were already in flight. Coaching trained that round.
What He Would Do Differently
- Practise solving out loud before the first onsite, not after HR
- Turn design chapters into timed spoken runs
- Use the same scaffold at every company — do not reinvent English per loop
- Treat stress as part of practice, not as a surprise on the day
Why This Matters for Tech Leads in Belgrade Interviewing in English
European loops still include a long spoken design and a coding narration. Leads who are calm in HR and chaotic in English lose senior roles they could do. The fix is performing the hard round in English until stress does not erase the plot.
Preparing for a similar path? Read How a Lead Backend Engineer Prepped for FAANG Interviews in English.
Other engineers practising interview English
Mockly has been the best investment I’ve made in the past year. The mentors don’t just have a deep knowledge of the language — they bring extensive experience in the IT industry. They understand the tech job market and are well-versed in modern engineering practices and the culture of top companies. Sessions aren’t just about improving your English; they’re an opportunity to sharpen your soft skills, gain valuable insights beyond engineering, and become a stronger communicator overall. Highly recommended.
Mockly knows what it takes to get hired. The preparation covers behavioral, algorithm, and system design interviews thoroughly — with real expertise in the STAR method, LeetCode, and Alex Xu’s system design frameworks. And when it comes to English and communication skills, the native-speaking mentors make all the difference.
Frequently Asked Questions
I pass HR but fail system design in English. What should I practise?
Timed spoken designs and LeetCode narration. HR success does not transfer.
How do I use system design books for interview English?
Say a chapter as a mock. Reading is not the skill the round grades.
I have several companies in process at once. Does that change prep?
Use one spoken scaffold everywhere. Company-specific trivia is cheaper than rebuilding English each time.
Should tech leads still practise LeetCode in English?
If the loop includes it, yes — out loud, under stress.
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