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.
What this case shows
A Belgrade senior engineer and tech lead could pass HR. Coaching focused on LeetCode and system design spoken in English under stress.
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
“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 and tech-lead seat, and a pile of management books. 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 class.
What We Practised
The hour looked like the round that scared him: a problem on the board, English on the delivery, and a stop when the plot disappeared. Design chapters became spoken drills. Behavioral stayed secondary.
- He practised LeetCode out loud under stress.
- He treated system design as a spoken performance using large-system examples.
- He did light behavioral practice for a tech-lead to manager pivot.
- He built English habits that transferred between companies already in process.
Useful references along the way: What to expect in English interviews, STAR interview framework.
Starting Point
He was based in Belgrade. An English-speaking job was the main goal. 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 live processes already in flight.
Before and After
Before coaching
- HR was easy; technical English was not.
- He could not focus on the solution while speaking.
- Stress destroyed fluency.
- He had multiple live processes with no stable spoken structure.
After coaching
- He used a LeetCode think-aloud checklist.
- He performed system design out loud, not only by reading chapters.
- He kept light behavioral practice for the lead and manager pivot.
- He used the 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 spoken structure 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.
Learning paths
Practise in the course
Start with your introOther 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.
FAQ
Questions
More questions? Email us at contact@mocklyenglish.com.
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